June 5, 2018

Breda, the Netherlands / Ghent, Belgium - argenx (Euronext & Nasdaq: ARGX), a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe autoimmune diseases and cancer, today announced that Euronext has selected argenx SE for inclusion in the BEL 20® Index on Euronext Brussels, effective June 18, 2018.

The BEL 20 Index represents the 20 largest companies traded on Euronext Brussels, subject to meeting Euronext Index Family criteria and review. For a complete overview of criteria and index rules, please see The Index Family Rulebook, at www.euronext.com.

"We are proud to be the fourth biotech company included in the BEL 20 Index, a clear indicator of the growing importance of the sector for the Belgian economy," commented Tim Van Hauwermeiren, CEO and co-founder of argenx. "We feel this inclusion also reflects our sustained growth as a company from our inception in 2008, through two public listings on Euronext Brussels and NASDAQ, into a world-class biotech company. To be listed among the largest public companies in Belgium is an honor and hopefully inspires a new generation of biotech entrepreneurs."

About argenxargenx is a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe autoimmune diseases and cancer. We are focused on developing product candidates with the potential to be either first-in-class against novel targets or best-in-class against known, but complex, targets in order to treat diseases with a significant unmet medical need. Our ability to execute on this focus is enabled by our suite of differentiated technologies. Our SIMPLE Antibody(TM) Platform, based on the powerful llama immune system, allows us to exploit novel and complex targets, and our three antibody engineering technologies are designed to enable us to expand the therapeutic index of our product candidates.

www.argenx.com For further information, please contact: Joke Comijn, Director Corporate Communications & Investor Relations (EU)+32 (0)477 77 29 44+32 (0)9 310 34 19info@argenx.com

Beth DelGiacco, VP Investor Relations (US)+1 518 424 4980info@argenx.com

Forward-looking Statements

The contents of this announcement include statements that are, or may be deemed to be, "forward-looking statements." These forward-looking statements can be identified by the use of forward-looking terminology, including the terms "believes," "estimates," "anticipates," "expects," "intends," "may," "will," or "should," and include statements argenx makes concerning the intended results of its strategy. By their nature, forward-looking statements involve risks and uncertainties and readers are cautioned that any such forward-looking statements are not guarantees of future performance. argenx's actual results may differ materially from those predicted by the forward-looking statements as a result of various important factors, including argenx's expectations regarding its the inherent uncertainties associated with competitive developments, preclinical and clinical trial and product development activities and regulatory approval requirements; argenx's reliance on collaborations with third parties; estimating the commercial potential of argenx's product candidates; argenx's ability to obtain and maintain protection of intellectual property for its technologies and drugs; argenx's limited operating history; and argenx's ability to obtain additional funding for operations and to complete the development and commercialization of its product candidates. A further list and description of these risks, uncertainties and other risks can be found in argenx's U.S. Securities and Exchange Commission (SEC) filings and reports, including in argenx's most recent annual report on Form 20-F filed with the SEC as well as subsequent filings and reports filed by argenx with the SEC. Given these uncertainties, the reader is advised not to place any undue reliance on such forward-looking statements. These forward-looking statements speak only as of the date of publication of this document. argenx undertakes no obligation to publicly update or revise the information in this press release, including any forward-looking statements, except as may be required by law.