Omeros Responds to Statnews.com Story SEATTLE, WA

Omeros Responds to Statnews.com Story

SEATTLE, WA August 23, 2017 Omeros Corporation (NASDAQ: OMER) stated today that it continues to pursue legal action to hold responsible

those behind a series of defamatory reports about the company posted online under the pseudonym Art Doyle, an entity or group that self-identifies as having a short position in Omeros stock. Because of its ongoing legal action,

including a number of steps aimed at unmasking the identity of the individual(s) responsible, Omeros elected not to respond to queries from a writer for statnews.com who evidently had early access to and commented through Twitter on the initial

Art Doyle false report before it was broadly made public.

While, for the reason stated above, Omeros will not engage in a running dialogue

with this writer, the company will respond this one time to correct some of the inaccuracies in yesterday s statnews.com story. Correct information is and has been publicly available to any individual wishing to obtain accurate background

Omeros accurately reports the status and results of its commercial, clinical and development programs and will continue its practice of

providing updates when appropriate.

About Omeros MASP Programs

Omeros controls the worldwide rights to MASP-2 and all therapeutics targeting MASP-2, a novel pro-inflammatory protein target involved in activation of the

complement system, which is an important component of the immune system. The complement system plays a role in the inflammatory response and becomes activated as a result of tissue damage or microbial infection. MASP-2 is the effector enzyme of the

lectin pathway, one of the principal complement activation pathways. Importantly, inhibition of MASP-2 does not appear to interfere with the antibody-dependent classical complement activation pathway, which is a critical component of the acquired

immune response to infection, and its abnormal function is associated with a wide range of autoimmune disorders. MASP-2 is generated by the liver and is then released into circulation. Adult humans who are genetically deficient in one of the

proteins that activate MASP-2 do not appear to be detrimentally affected by the deficiency. OMS721 is Omeros lead human MASP-2 antibody.

Following discussions with both the FDA and the European Medicines Agency, a Phase 3 clinical program for OMS721

in atypical hemolytic uremic syndrome (aHUS) is in progress. A second Phase 3 clinical program for OMS721 has been initiated in immunoglobulin A (IgA) nephropathy. Also, two Phase 2 trials are ongoing. One is continuing to enroll OMS721 in IgA

nephropathy following an earlier Phase 2 trial that generated positive data in patients with IgA nephropathy and with lupus nephritis; the other is enrolling and has reported positive data both in patients with hematopoietic stem cell

transplant-associated thrombotic microangiopathy (TMA). A third Phase 3 program could begin later this year in stem cell transplant-associated TMA. OMS721 can be administered both intravenously and subcutaneously, and Omeros expects to commercialize

each formulation of OMS721 for different therapeutic indications. In parallel, Omeros is developing small-molecule inhibitors of MASP-2. Based on requests from treating physicians, Omeros has established a compassionate-use program for OMS721, which

is active in both the U.S. and Europe. The FDA has granted OMS721 breakthrough therapy designation for IgA nephropathy, orphan drug status for the prevention (inhibition) of complement-mediated TMAs and for the treatment of IgA nephropathy, and fast

track designation for the treatment of patients with aHUS.

Omeros also has identified MASP-3 as responsible for the conversion of pro-factor D to factor

D and as a critical activator of the human complement system s alternative pathway. The alternative pathway is linked to a wide range of immune-related disorders. In addition to its lectin pathway inhibitors, the company is advancing its

development of antibodies and small-molecule inhibitors against MASP-3 to block activation of the alternative pathway. Omeros is preparing to initiate manufacturing scale-up of its MASP-3 antibodies in advance of clinical trials.

About Omeros Corporation

Omeros is a commercial-stage

biopharmaceutical company committed to discovering, developing and commercializing small-molecule and protein therapeutics for large-market as well as orphan indications targeting inflammation, complement-mediated diseases and disorders of the

central nervous system. The company s drug product OMIDRIA (phenylephrine and ketorolac injection) 1% / 0.3% is marketed for use during cataract surgery or intraocular lens (IOL)

replacement to maintain pupil size by preventing intraoperative miosis (pupil constriction) and to reduce postoperative ocular pain. In the European Union, the European Commission has approved OMIDRIA for use in cataract surgery and other IOL

replacement procedures to maintain mydriasis (pupil dilation), prevent miosis (pupil constriction), and to reduce postoperative eye pain. Omeros has multiple Phase 3 and Phase 2 clinical-stage development programs focused on: complement-associated

thrombotic microangiopathies; complement-mediated glomerulonephropathies; Huntington s disease and cognitive impairment; and addictive and compulsive disorders. In addition, Omeros has a diverse group of preclinical programs and a proprietary G

protein-coupled receptor (GPCR) platform through which it controls 54 new GPCR drug targets and corresponding compounds, a number of which are in preclinical development. The company also exclusively possesses a novel antibody-generating platform.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the

Securities Exchange Act of 1934, which are subject to the safe harbor created by those sections for such statements. All statements other than statements of historical fact are forward-looking statements, which are often indicated by

terms such as anticipate, believe, could, estimate, expect, goal, intend, look forward to, may, plan, potential,

predict, project, should, will, would and similar expressions and variations thereof. Forward-looking statements are based on management s beliefs and assumptions and on information

available to management only as of the date of this press release. Omeros actual results could differ materially from those anticipated in these forward-looking statements for many reasons, including, without limitation, risks associated with

product commercialization and commercial operations, unproven preclinical and clinical development activities, regulatory oversight, intellectual property claims, competitive developments, litigation, and the risks, uncertainties and other factors

described under the heading Risk Factors in the company s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on August 8, 2017. Given these risks, uncertainties and other factors, you should not

place undue reliance on these forward-looking statements, and the company assumes no obligation to update these forward-looking statements, even if new information becomes available in the future.

Jennifer Cook Williams

Cook Williams Communications, Inc.

Investor and Media Relations