Achillion Pharmaceuticals Announces Proposed Public Offering of Common Stock

Achillion Pharmaceuticals Announces Proposed Public Offering of Common Stock

NEW HAVEN, Conn., Feb. 20, 2013 (GLOBE NEWSWIRE) -- Achillion Pharmaceuticals,
Inc. (Nasdaq:ACHN) announced today that it has commenced an underwritten
public offering of $125 million of its common stock. In connection with this
offering, Achillion plans to grant the underwriters a 30-day option to
purchase additional shares of its common stock. Citigroup and Leerink Swann
LLC are acting as joint book-running managers for the offering. The offering
is subject to market conditions, and there can be no assurance as to whether
or when the offering may be completed, or as to the actual size or terms of
the offering.

The offering is being made by Achillion pursuant to a shelf registration
statement on Form S-3 previously filed with the Securities and Exchange
Commission (SEC), which the SEC declared effective on November 21, 2012. A
preliminary prospectus supplement related to the offering will be filed with
the SEC and will be available on the SEC's website located at Copies of the preliminary prospectus supplement and
accompanying prospectus relating to this offering may be obtained from
Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue,
Edgewood, NY 11717, via telephone at 1-800-831-9146 or email at or from Leerink Swann LLC, Attention: Syndicate
Department, One Federal Street, 37th Floor, Boston, MA 02110, via telephone
number (800) 808-7525, Ext. 4814, or email at

This press release shall not constitute an offer to sell, or the solicitation
of an offer to buy, nor will there be any sale of, these securities in any
state or other jurisdiction in which such offer, solicitation or sale would be
unlawful prior to the registration or qualification under the securities laws
of such state or other jurisdiction.

About Achillion Pharmaceuticals, Inc.

Achillion is an innovative pharmaceutical company dedicated to bringing
important new treatments to patients with infectious disease.

Forward-Looking Statements

This press release includes "forward-looking statements" made under the
provisions of the Private Securities Litigation Reform Act of
1995.Forward-looking statements include statements, other than statements of
historical fact, regarding, without limitation, the completion, timing and
size of Achillion's proposed public offering and the use of proceeds
therefrom.In some cases, words such as "will," "expect" or other comparable
words identify forward-looking statements.Actual results, performance or
experience may differ materially from those expressed or implied by any
forward-looking statement as a result of various important factors, including
without limitation risks and uncertainties relating to Achillion's business
and financial condition, general market conditions and the satisfaction of
customary closing conditions associated with the proposed public
offering.Factors that may cause such a difference include, without
limitation, risks and uncertainties related to whether or not Achillion will
be able to raise capital through the sale of shares of common stock, the final
terms of the proposed offering, market and other conditions, the satisfaction
of customary closing conditions related to the proposed public offering and
the impact of general economic, industry or political conditions in the United
States or internationally. Risks and uncertainties that Achillion faces are
described in greater detail under the heading "Risk Factors" in its 2012
Annual Report on Form 10-K and its subsequent SEC filings, as well as other
filings that it makes with the SEC. As a result of the risks and
uncertainties, the results or events indicated by any forward-looking
statement may not occur. Achillion cautions you not to place undue reliance on
any forward-looking statement.

In addition, any forward-looking statement in this press release represents
Achillion's views only as of the date of this press release and should not be
relied upon as representing its views as of any subsequent date. Achillion
disclaims any obligation to update any forward-looking statement, except as
required by applicable law.

CONTACT: Company Contact:
         Glenn Schulman
         Achillion Pharmaceuticals, Inc.
         Tel. (203) 624-7000
         Christin Culotta Miller
         Ogilvy PR
         Tel. (212) 880-5264
         Mary Kay Fenton
         Achillion Pharmaceuticals, Inc.
         Tel. (203) 624-7000
         Seth Lewis
         The Trout Group, LLC
         Tel. (646) 378-2952
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