Since 2011, the New York City (NYC) Department of Health and Mental Hygiene (DOHMH) has typically been notified of three or fewer cases of hepatitis A virus (HAV) infection each year among men who have sex with men (MSM) who reported no travel to countries where HAV is endemic. This year, DOHMH noted an increase in HAV infections among MSM with onsets in January-March 2017, and notified other public health jurisdictions via Epi-X, CDC's communication exchange network. As a result, 51 patients with HAV infection involving MSM were linked to the increase in NYC.