Exhibit 99.1

National Interstate Corporation Closes on $100 Million Bank Credit Facility

Richfield, Ohio, November 19, 2012 – National Interstate Corporation (Nasdaq: NATL) announced today that it has entered into a $100 million five year unsecured Credit Agreement with Fifth Third Bank, as administrative agent and lead arranger, and U.S. Bank National Association, as documentation agent. The Company has the ability to increase the line of credit to $125 million subject to the Agreement’s accordion feature. The Credit Agreement replaces an existing $50 million credit facility.

“Our history of profitable underwriting and investment results has provided us with adequate capital to fund our growing business and our positive cash flows allowed us to maintain a relatively low debt to equity ratio,” commented Julie McGraw, Vice President and Chief Financial Officer. “This new line of credit will provide us with a significant source of backup liquidity, further bolstering our strong balance sheet. Through the support of our strong lending group, we closed our financing with what we believe to be very attractive terms and are positioned for the long-term with greater financial flexibility that will allow us to capitalize on strategic opportunities as they arise.”

As of September 30, 2012, National Interstate’s debt to total equity ratio was 5.7%. The credit facility may be used for general corporate purposes, including items such as working capital and acquisitions.

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@natl.com

www.natl.com