The Pennsylvania Department of Health and CDC are investigating an outbreak of hepatitis A outbreak among patrons of a restaurant (Restaurant A) in Monaca, Pennsylvania. As of November 20, approximately 555 persons with hepatitis A have been identified, including at least 13 Restaurant A food service workers and 75 residents of six other states who dined at Restaurant A. Three persons have died. Preliminary sequence analysis of a 340 nucleotide region of viral RNA obtained from three patrons who had hepatitis A indicated that all three virus sequences were identical. Preliminary analysis of a case-control study implicated green onions as the source of the outbreak.