Exhibit 99.1

National Interstate Corporation Reports 2011 Third Quarter Results and Quarterly Dividend

Richfield, Ohio, November 1, 2011 — National Interstate Corporation (Nasdaq: NATL) today reported results for the 2011 third quarter and first nine months. Gross premiums written of $120.9 million for the 2011 third quarter and $411.7 million for the 2011 first nine months increased 3.7% and 23.6%, respectively, compared to the same periods last year. Both periods reflect growth in existing businesses and the first nine months also include the favorable impact from the acquisition of Vanliner Insurance Company in July 2010. Net after-tax earnings from operations per share, diluted of $.31 for the 2011 third quarter decreased and $1.22 for the 2011 first nine months was flat compared to the same prior year periods. Both 2011 periods had higher net investment income offset by lower underwriting profits.

“Our top line has performed consistently well throughout the year with growth in existing businesses and the favorable impact of the Vanliner premium,” stated Dave Michelson, President and Chief Executive Officer. “2011 third quarter earnings from operations included the adverse impact of approximately $.26 per share related to claims costs above those experienced in the 2010 third quarter for our recreational vehicle (RV) product line and two Alternative Risk Transfer (ART) programs. Weather related losses comprised approximately 20% of this unusual claims variance. “

Gross Premiums Written

Mr. Michelson commented, “The addition of the Vanliner business accounts for much of the 23.6% year over year growth. However, we have also grown our existing business in 2011. For the first time since the acquisition both the 2011 and 2010 quarterly results include Vanliner business and we reported a 3.7% increase in gross premiums written.”

The table below summarizes gross premiums written by business component:

Alternative Risk Transfer (ART): The ART component grew 17% for the 2011 third quarter and 24% for the 2011 first nine months compared to the same 2010 periods. The growth in this component was attributable to the continued above average customer retention combined with the addition of new customers in existing programs. Underwriting actions for the two previously mentioned ART programs that experienced elevated claims in the 2011 third quarter and which comprise approximately 9% of our total in-force premiums, may adversely affect future growth in this component. However, the Company expects the ART component to continue to be a primary growth source, with continued expansion of existing programs and the development of new products.

Transportation: Beginning in the 2010 third quarter, traditional business written as a result of the Vanliner acquisition was reported in the Transportation component. The growth in this component during the first half of this year was attributable to moving and storage premiums that have been written through Vanliner. For the 2011 third quarter, this component declined approximately 4% primarily due to non-moving and storage 2010 premiums, written in conjunction with the Vanliner balance sheet guarantee, that the Company chose not renew. Business being generated by the Company’s other transportation products in this component have been flat to down in 2011 when compared to 2010.

Specialty Personal Lines: Gross premiums written in the specialty personal lines component have declined in each of the first three quarters of 2011. Underwriting and pricing actions in 2010 related to the commercial vehicle product and a decline in quotes in 2011for the RV product have adversely affected the top line for this component.

Hawaii and Alaska: This component has experienced growth for two consecutive quarters with gross premiums moderately ahead of the first nine months of 2010. The Company is encouraged but cautiously optimistic as market conditions remain competitive.

Earnings

The table below shows the Company’s net income determined in accordance with U.S. generally accepted accounting principles (GAAP), reconciled between several non-GAAP financial measures to better reflect the results related to the ongoing business.

Net after-tax earnings from operations are comprised of underwriting income and net investment income. The Company separately reports after-tax realized gain from investments and the after-tax impact on underwriting results related to the balance sheet guaranty and gain on bargain purchase from the Vanliner acquisition.

Underwriting Results:

The following ratios exclude the impact from the balance sheet guaranty associated with the Vanliner acquisition to reflect the results of ongoing underwriting operations:

The Company has experienced higher combined ratios throughout 2011 compared to 2010. The underwriting results for the first nine months of 2011 reflect higher claims costs and slightly lower underwriting expenses. The prolonged competitive commercial market conditions have contributed to rising loss and loss adjustment expense (LAE) ratios in 2011. Both claims costs and underwriting expenses were elevated in the 2011 third quarter as discussed below:

Claims: Historically the Company has experienced higher claims costs in the third quarter because of weather events and driving patterns of their customers. The 2011 third quarter loss and LAE ratio increased 4.1 percentage point compared to the 2010 third quarter. During the 2011 third quarter the Company’s RV product added approximately 2.2 percentage points to the 2011 third quarter loss and LAE ratio due to unusually high weather (1.4 points) and fire (.8 points) related claims. In addition, elevated claims costs in two ART programs when compared to the prior year added approximately 5.2 percentage points to the 2011 third quarter loss and LAE ratio. One of the programs is in the process of winding down while the other has recently undergone corrective underwriting actions. Other products are performing within expected ranges for both the 2011 third quarter and first nine months.

For the 2011 third quarter the Company had favorable development from prior year claims of $0.8 million which reduced the loss and LAE ratio by 0.7 percentage points. This compares to 2.2 percentage points of favorable development for the 2010 third quarter.

Underwriting Expenses: The Company’s quarterly underwriting expense ratios often vary based on the mix of business written or non-recurring items. The 2011 third quarter underwriting expense ratio is within the expected range while the 2010 third quarter ratio is lower because of the favorable impact related to adjustments to variable employee expenses.

Mr. Michelson said, “While we expect an up-tick in claims during the third quarter, we are not satisfied with the 2011 third quarter underwriting results. As a specialty niche underwriter we manage many unique insurance programs and continually make adjustments to them. Actions have been taken in the two ART programs which contributed to the elevated third quarter losses and we believe the RV losses were an aberration. The insurance markets remain competitive, but the atmosphere where rate decreases are expected appears to be ending. We continue to target low to mid 90’s combined ratios in the current insurance environment.”

Investments:

Net investment income of $22.3 million for the 2011 first nine months increased 36% compared to the 2010 first nine months reflecting the addition of the Vanliner portfolio in July 2010. Net investment income of $7.6 million for the 2011 third quarter was 18% above the 2010 third quarter primarily due to repositioning of the acquired Vanliner portfolio in higher yielding investments.

The Company had net realized gain from investments of $2.9 million for the 2011 first nine months primarily from security sales at gains for reinvestment in higher yielding sectors. The net realized gains of $3.5 million for the 2010 first nine months were from sales to generate funds for the Vanliner acquisition.

The Company maintains a high quality and diversified portfolio with approximately 89% of its cash and invested assets rated as investment grade and an average rating of AA- in its fixed income portfolio. The fair value and unrealized gains (losses) of fixed maturities and equity securities were as follows:

Impact from the Vanliner Guaranteed Runoff Business and Deferred Income Tax Valuation Allowance:

As previously disclosed, the seller of Vanliner provided National Interstate with comprehensive financial guarantees related to the runoff of Vanliner’s final closing balance sheet whereby both favorable and unfavorable balance sheet development inures to the seller. Additionally, as a result of purchase accounting requirements the Company was required to determine the fair value of the future economic benefit of the financial guarantees and acquired loss reserves, as of the date of acquisition and record it as a $7.5 million gain on bargain purchase, despite the fact that actual gains and losses related to the financial guaranty will be reflected in operations as they are incurred in future periods. As a result, the timing of the revenues and expenses associated with the guaranteed runoff business will not occur in the same period and will result in combined ratios which are not consistent with the negotiated combined ratio which was to approximate 100% for the Vanliner guaranteed business. As such, the after-tax impact from the runoff business guaranteed by the seller of $0.4 million and $2.1 million for the 2011 third quarter and first nine months respectively, have been removed from the net after-tax earnings from operations to reflect only those results of the ongoing business.

In 2008, the Company established a valuation allowance on deferred tax assets associated with its net realized investment losses, primarily impairment charges during the financial crisis, which increased the 2008 effective tax rate. Beginning in the 2009 first quarter and continuing through the 2010 first quarter, this valuation allowance decreased resulting in a corresponding decrease in the federal income tax expense. No valuation allowance against deferred tax assets existed subsequent to March 31, 2010.

Quarterly Dividend

The Company’s Board of Directors approved a quarterly dividend of $0.09 per share on October 27, 2011. The cash dividend will be payable on December 12, 2011 to shareholders of record of the Company’s common stock as of the close of business on November 28, 2011.

Earnings Conference Call

The Company will hold a conference call to discuss the 2011 third quarter results tomorrow, Wednesday, November 2, 2011 at 10:00 a.m. Eastern Time. There are two communication modes available to listen to the call. Telephone access to the conference call and Q and A session will be available by dialing 888-713-8566 and providing the confirmation code 88357105. Please dial in 5 to 10 minutes prior to the scheduled starting time. The conference call will be broadcast live over the Internet. To listen to the call via the Internet, access our website at http://invest.natl.com and follow the instructions at the web cast link. The archived web cast will be available shortly after the call on our website.

Forward-Looking Statements

This document, including any information incorporated by reference, contains “forward-looking statements” (within the meaning of the Private Securities Litigation Reform Act of 1995). All statements, trend analyses and other information contained in this press release relative to markets for our products and trends in our operations or financial results, as well as other statements including words such as “may,” “target,” “anticipate,” “believe,” “plan,” “estimate,” “expect,” “intend,” “project,” and other similar expressions, constitute forward-looking statements. We made these statements based on our plans and current analyses of our business and the insurance industry as a whole. We caution that these statements may and often do vary from actual results and the differences between these statements and actual results can be material. Factors that could contribute to these differences include, among other things: general economic conditions, any weaknesses in the financial markets and other factors, including prevailing interest rate levels and stock and credit market performance which may affect or continue to affect (among other things) our ability to sell our products and to collect amounts due to us, our ability to access capital resources and the costs associated with such access to capital and the market value of our investments; our ability to manage our growth strategy, customer response to new products and marketing initiatives; tax law and accounting changes; increasing competition in the sale of our insurance products and services and the retention of existing customers; changes in legal environment; regulatory changes or actions, including those relating to regulation of the sale, underwriting and pricing of insurance products and services and capital requirements; levels of natural catastrophes, terrorist events, incidents of war and other major losses; adequacy of insurance reserves; and availability of reinsurance and ability of reinsurers to pay their obligations. The forward-looking statements herein are made only as of the date of this document. The Company assumes no obligation to publicly update any forward-looking statements.

About National Interstate Corporation

An Insurance Experience Built Around You.

National Interstate Corporation (Nasdaq: NATL), founded in 1989, is the holding company for a specialty property-casualty insurance group which differentiates itself by offering products and services designed to meet the unique needs of niche markets. Products include insurance for passenger, truck, and moving and storage transportation companies, alternative risk transfer, or captive programs for commercial risks, specialty personal lines products focused primarily on recreational vehicle owners and small commercial vehicle accounts, and transportation and general commercial insurance in Hawaii and Alaska. The Company’s insurance subsidiaries, including the three primary insurers, National Interstate Insurance Company, Vanliner Insurance Company and Triumphe Casualty Company, are rated “A” (Excellent) by A.M. Best Company. Headquartered in Richfield, Ohio, National Interstate is an independently operated subsidiary of Great American Insurance Company, a property-casualty subsidiary of American Financial Group, Inc. (NYSE: AFG) (Nasdaq: AFG).

Contact:

Tanya Inama

National Interstate Corporation

877-837-0339

investorrelations@nationalinterstate.com

www.natl.com

NATIONAL INTERSTATE CORPORATION

SELECTED FINANCIAL DATA

(In thousands, except per share data)