Omeros Corporation Reports Fourth Quarter and Year-End 2017 Financial Results - Conference Call Today at 4:30 p.m. ET - SEATTLE, WA

Omeros Corporation Reports Fourth Quarter and Year-End 2017 Financial Results

- Conference Call Today at 4:30 p.m. ET -

SEATTLE, WA - March 1, 2018 - Omeros Corporation (NASDAQ: OMER), 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, today announced recent highlights and developments as well as financial results for the fourth quarter and year ended December 31, 2017, which include:

"The company's progress during the fourth quarter of 2017 continued to build on our accomplishments earlier in the year," said Gregory A. Demopulos, M.D., chairman and chief executive officer of Omeros. "Following consistently positive OMS721 data, we now have three ongoing Phase 3 clinical programs - IgA nephropathy, aHUS and, most recently, stem-cell TMA. With breakthrough therapy, fast track and orphan designations across these indications, we are continuing our interactions with FDA and European regulatory authorities to expedite approval pathways and, in the near term, to discuss accelerated and conditional approvals in stem-cell TMA. Next up is OMS527, on track to enter the clinic in mid-year for the treatment of nicotine addiction. Our frustration, shared by physicians nationwide, remains patients' restricted access to OMIDRIA following its pass-through expiration on January 1. Congressional and administrative efforts are ongoing, and we look forward to resolving this issue soon. We are confident that OMIDRIA in 2018 will continue to fuel the advancement of our pipeline and OMS721 toward commercialization, helping to save lives."

Fourth Quarter and Recent Developments

For the quarter ended December 31, 2017, revenues were $13.8 million, all relating to sales of OMIDRIA. This compares to OMIDRIA revenues of $12.9 million for the same period in 2016. On a sequential quarter-over-quarter basis, OMIDRIA revenue decreased $7.9 million, or 36.5%, despite the fact that unit pricing and the total number of vials sold to ASCs and hospitals was unchanged from the quarter ended September 30, 2017. Under the company's accounting policies, it is not able to recognize a majority of the revenue related to OMIDRIA inventories held by wholesalers at year end because of uncertainty around OMIDRIA reimbursement following expiration of pass-through status on January 1, 2018 and resulting reduced first quarter sell-through. In addition, a $2.4 million charge to revenue was recorded in the fourth quarter for vials that the company reserved for returns by the ASCs and hospitals anticipated in 2018.

Total operating costs and expenses for the three months ended December 31, 2017 were $27.9 million compared to $24.8 million for the same period in 2016. The change in the current year quarter was primarily due to higher third-party manufacturing scale up costs for our OMS721 program and higher third-party development expenses for our product candidates.

For the three months ended December 31, 2017, Omeros reported a net loss of $16.6 million, or $0.34 per share, again reflecting the inability to recognize wholesaler inventories at year end and which included non-cash expenses of $4.5 million ($0.09 per share). This compares to the prior year's fourth quarter when Omeros reported a net loss of $19.6 million, or $0.45 per share, which included non-cash expenses of $5.2 million ($0.12 per share). The reduction in cash, cash equivalents and short-term investments from the third quarter to the fourth quarter was $3.1 million.

As of December 31, 2017, the company had $83.7 million of cash, cash equivalents and short-term investments available for operations and $5.8 million in restricted cash, with an additional $17.1 million in accounts receivable. The company also has the ability, at its sole discretion, to borrow $45.0 million from its existing lenders through May 20, 2018, subject to customary closing conditions.

Revenues for the full year 2017 were $64.8 million, a 55.8% increase compared to $41.6 million for the full year 2016. The increase was primarily attributable to an increase in both new customers and increased OMIDRIA purchases from our existing customers.

Total operating costs and expenses for the year ended December 31, 2017 were $108.7 million, an increase of $12.8 million compared to 2016. The 2017 increase related primarily to higher third-party manufacturing scale up costs for our OMS721 program, higher third-party development expenses for our product candidates, and higher legal expenses incurred in the defense of our patent infringement lawsuit against Par that was settled favorably in October 2017.

For the full year 2017, Omeros reported a net loss of $53.5 million, or $1.17 per share, including non-cash expenses of $17.4 million, or $0.38 per share. This compares to a net loss of $66.7 million, or $1.65 per share in 2016, including non-cash expenses of $16.1 million, or $0.40 per share.

Conference Call Details

Omeros' management will host a conference call to discuss the financial results and to provide an update on business activities. The call will be held today at 1:30 p.m. Pacific Time; 4:30 p.m. Eastern Time. To access the live conference call via phone, please dial (844) 831-4029 from the United States and Canada or (920) 663-6278 internationally. The participant passcode is 1759244. Please dial in approximately 10 minutes prior to the start of the call. A telephone replay will be available for one week following the call and may be accessed by dialing (855) 859-2056 from the United States and Canada or (404) 537-3406 internationally. The replay passcode is 1759244.

To access the live or subsequently archived webcast of the conference call on the internet, go to the company's website at www.omeros.com and select "Events" under the Investors section of the website. To access the live webcast, please connect to the website at least 15 minutes prior to the call to allow for any software download that may be necessary.

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 intraocular solution) 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," "likely," "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 Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 1, 2018. 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

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)

UNAUDITED CONSOLIDATED BALANCE SHEET DATA