Exhibit 99.1

3050 Spruce Street, St. Louis, MO 63103 USA

Tel: (800) 521-8956 (314) 771-5765 Fax: (800) 325-5052 (314) 771-5757

FOR IMMEDIATE RELEASE -St. Louis, MO., April 26, 2011

SIGMA-ALDRICH (NASDAQ:SIAL) REPORTS Q1 2011 DILUTED EPS OF $0.97, A 20%

INCREASE OVER Q1 2010. Q1 2011 SALES AND EARNINGS ACHIEVE NEW

QUARTERLY HIGH. FULL YEAR 2011 DILUTED ADJUSTED EPS EXPECTATION

RAISED TO $3.60 TO $3.75.

HIGHLIGHTS:

2011 Results (all percentages are to comparable periods in 2010)

2011 Outlook (all percentages are compared to full year 2010 results)

CEO’s STATEMENT:

Commenting on first quarter 2011 performance, President and CEO Rakesh Sachdev said: “Our reported sales of $632 million and diluted EPS of $0.97 for the first quarter of 2011 were the best reported quarterly results in our history. We are very pleased with this strong performance as we begin 2011. Our SAFC sales grew by 16% on an organic basis driven by continued strong demand for materials and precursors for semi-conductor and L.E.D. applications and for industrial cell culture

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media used for producing biological drugs. Our research initiatives in analytical chemistry, biology, traditional chemistry and materials science, coupled with a 2% acquisition benefit to expand our analytical chemistry offering, helped achieve currency adjusted growth of 6% in our Research business.

We continued to expand our product offering with the addition of over 3,000 high quality analytical reference standards through the acquisitions of Cerilliant Corporation and Resource Technology Corporation, a new suite of knockout rats to model Parkinson’s disease, new diagnostic raw materials for point of care and over the counter diagnostic kits and the addition of 1,400 new cell lines from the European Cell Culture Collection. We also launched the first phase of our new web site with an enhanced scientific workflow to help researchers more easily find information, tools, products and services needed to accelerate research and discovery.”

Sachdev continued, “We’ve reaffirmed our organic sales growth expectation for 2011 of mid-single digit percentage growth. This organic growth, along with benefits from currency and acquisitions are expected to drive overall growth to low double digits. We’ve also raised our diluted adjusted EPS outlook for 2011 to a new range of $3.60 to $3.75 as a result of stronger operational performance in the first quarter and more favorable foreign currency exchange rates. Our commitment to continuous improvement is expected to ensure that we deliver flawless execution of our strategic initiatives to drive sales of our analytical chemistry, biology, traditional chemistry and materials science products, to deliver high single digit organic growth in SAFC for the full year and to enhance our e-commerce and Asia Pacific-Latin American market sales. All of these efforts are intended to boost sales growth above the underlying market rate. Let me assure you that our management team is fully engaged and committed to deliver this performance.”

2011 RESULTS:

Reported sales for the first quarter of 2011 of $632 million increased 10% from the first quarter of 2010. Excluding changes in foreign currency exchange rates and acquisitions that increased overall sales by 2% and 1%, respectively, first quarter organic sales growth was 7%. First quarter sales for the Company’s Research business grew organically by 4% with organic sales growth in the Asia Pacific-Latin American and European markets of 7% and 4%, respectively. First quarter sales for the Company’s SAFC business grew 16% on a currency-adjusted basis as sales of our Supply Solutions, Bioscience and Hitech products again reflected stronger demand. A reconciliation of reported to adjusted (organic) sales is on page 8.

The operating income margin in the first quarter of 2011 was 26.4% of sales, compared to 25.7% of sales reported in the first quarter of 2010. Excluding restructuring costs, the operating income margin in the first quarter of 2011 was 26.9%, roughly in line with the 26.7% adjusted operating margin achieved in the first quarter of 2010. During the first quarter of 2011, we made additional investments of $3 million in initiatives that are expected to drive future sales growth at above market rates and in operational improvements including the opening of a European Headquarters in Switzerland. Restructuring costs of $3 million in 2011’s first quarter related to the previously announced consolidation of certain manufacturing facilities in the U.S. and Europe. These restructuring actions reflect the Company’s efforts to improve operating efficiencies and lower its fixed cost structure as part of a longer term goal to improve operating margins.

The effective tax rate for the first quarter of 2011 was 27.9% compared to 31.0% in the first quarter of 2010. The lower tax rate in the first quarter of 2011 resulted from the resolution and related release of certain tax contingencies amounting to $0.04 per diluted share. A non-recurring income tax charge in the first quarter of 2010 related to the non-deductibility of expenses reimbursed under Medicare Part D drove that period’s tax rate to 31%. The effective tax rate for all of 2011 is expected to be approximately 29% to 30% of pretax income.

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Free cash flow (defined on page 7) for the first quarter of 2011 was $133 million, comparable to that in the first quarter of 2010. Higher net income was largely offset by a higher level of working capital to support growth in the faster growing international markets. A reconciliation of net cash provided by operating activities to free cash flow is on page 9.

Other highlights from global sales growth initiatives include:

2011 OUTLOOK:

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OTHER INFORMATION:

Cash Flow and Debt: Net cash provided by operating activities for the first quarter of 2011 was $151 million, comparable to the first quarter of 2010. Higher net income and non-cash charges in the first quarter of 2011 compared to the first quarter of 2010 were largely offset by higher uses of cash for accounts receivable and inventory. Capital expenditures in the first quarter of each of 2011 and 2010 were $18 million. Inventory levels were 6.5 months at March 31, 2011 compared to 6.2 months at March 31, 2010, in line with expectations. Free cash flow of $133 million for the first quarter of 2011 was used to return $43 million to shareholders through share repurchases and dividends, repay $50 million in debt and fund acquisitions of $20 million. The Company’s debt to capital ratio was reduced to 19% at March 31, 2011 from 21% at December 31, 2010.

Share Repurchase: Another 0.3 million shares were acquired in the first quarter of 2011 at an average share price of $62.95. There were 122 million shares outstanding at March 31, 2011. The Company expects to continue to offset the dilutive impact of issuing share based incentive compensation with future repurchases. The Company may repurchase additional shares, but the timing and amount will depend upon market conditions and other factors.

Cautionary Statement: This release contains forward-looking statements relating to future performance, goals, strategic actions and initiatives and similar intentions and beliefs, including phrases “is expected”, “reaffirmed,”, “plans”, “to drive”, “to boost”, “to enhance”, “are intended” and other statements regarding the Company’s expectations, goals, beliefs, intentions and the like regarding future sales, earnings, free cash flow, share repurchases, acquisitions and other matters. These statements are based on assumptions regarding Company operations, investments and acquisitions and conditions in the markets the Company serves. The Company believes these assumptions are reasonable and well founded. The forward-looking statements in this release are subject to risks and uncertainties, including, among others, certain economic, political and technological factors. Actual results could differ materially from those stated or implied in this news release, due to, but not limited to, such factors as (1) global economic conditions, (2) changes in pricing and the competitive environment and the global demand for our products, (3) fluctuations in foreign currency exchange rates, (4) changes in research funding and the success of research and development activities, (5) failure of planned sales initiatives in our Research and SAFC businesses, (6) dependence on uninterrupted manufacturing operations, (7) failure to achieve planned cost reductions in global supply chain initiatives and restructuring actions, (8) changes in the regulatory environment in which the Company operates, (9) changes in worldwide tax rates or tax benefits from domestic and international operations, including the matters described in Note 10-Income Taxes-to the Consolidated Financial Statements in the Company’s Form 10-K report for the year ended December 31, 2010, (10) exposure to litigation, including product liability claims, (11) the ability to maintain adequate quality standards, (12) reliance on third party package delivery services, (13) an unanticipated increase in interest rates, (14) other changes in the business environment in which the Company operates, and (15) the outcome of the outstanding matters described in Note 11-Contingent Liabilities and Commitments-to the Consolidated Financial Statements in the Company’s Form 10-K report for the year ended December 31, 2010. A further discussion of the Company’s risk factors can be found in Item 1A of Part 1 of the Company’s Form 10-K report for the year ended December 31, 2010. The Company does not undertake any obligation to update these forward-looking statements.

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About Sigma-Aldrich: Sigma-Aldrich is a leading Life Science and High Technology company. Our biochemical and organic chemical products and kits are used in scientific research, including genomic and proteomic research, biotechnology, pharmaceutical development, and as key components in pharmaceutical, diagnostic and other high technology manufacturing. We have customers in life science companies, university and government institutions, hospitals and in industry. Over one million scientists and technologists use our products. Sigma-Aldrich operates in 40 countries and has 8,000 employees providing excellent service worldwide. We are committed to accelerating our Customers’ success through leadership in Life Science, High Technology and Service. For more information about Sigma-Aldrich, please visit our award winning web site at www.sigma-aldrich.com.

Non-GAAP Financial Measures: The Company supplements its disclosures made in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) with certain non-GAAP financial measures. The Company does not, and does not suggest investors should, consider such non-GAAP financial measures in isolation from, or as a substitute for, GAAP financial information. These non-GAAP measures may not be consistent with the presentation by similar companies in the Company’s industry. Whenever the Company uses such non-GAAP measures, it provides a reconciliation of such measures to the most closely applicable GAAP measure. See the Supplemental Financial Information on pages 8 and 9 for these reconciliations.

With over 60% of sales denominated in currencies other than the U.S. dollar, management uses currency adjusted growth, and believes it is useful to investors, to judge the Company’s local currency performance. Organic sales growth data presented in this release excludes currency and acquisitions impacts. The Company calculates the impact of changes in foreign currency rates by multiplying current period activity by the difference between current period exchange rates and prior period exchange rates, the result is the defined impact of “changes in foreign currency exchange rates”. While we are able to report currency impacts after the fact, we are unable to estimate changes that may occur later in 2011 to applicable exchange rates. Any significant changes in currency exchange rates would likely have a significant impact on our reported growth rates due to the volume of our sales denominated in foreign currencies.

Management also uses adjusted net income and EPS and adjusted operating income and operating income margins (reconciled on page 9) and free cash flow (defined on page 7), non-GAAP measures, to judge its performance and ability to pursue opportunities that enhance shareholder value. Due to the uncertain timing of future restructuring and other extraordinary special charges, we are unable to include these charges in the 2011 diluted adjusted EPS forecast or provide a reconciliation to the corresponding GAAP measures. Management believes this non-GAAP information is useful to investors as well.

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SIGMA-ALDRICH CORPORATION

Consolidated Statements of Income (Unaudited)

(in millions except per share amounts)

SIGMA-ALDRICH CORPORATION

Consolidated Balance Sheets

(in millions)

6

SIGMA-ALDRICH CORPORATION

Consolidated Statements of Cash Flows (Unaudited)

(in millions)

7

SIGMA-ALDRICH CORPORATION

Supplemental Financial Information—(Unaudited)

Sales Growth by Business Unit

Business Unit Sales

(in millions)

8

SIGMA-ALDRICH CORPORATION

Supplemental Financial Information - (Unaudited)

Reconciliation of Reported Net Income to Adjusted Net Income

Income Statement Ratios

Reconciliation of Reported Operating Income to Adjusted Operating Income

(in millions)

Reconciliation of Free Cash Flow

(in millions)

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