Acute hepatitis patients admitted to a referral centre from January 1995 through December 1995 were studied to determine the seroprevalence of the hepatitis viruses and related risk factors. Of the 434 patients with acute viral hepatitis, the episodes due to hepatitis A, B, C, D, and non-A, non-B, non-C, (non-ABC) were 214 (49.3%), 163 (37.6%), 7 (1.6%), 0 (0%), and 50 (11.5%), respectively. Acute hepatitis A and non-ABC hepatitis commonly occur in late spring and early summer and are probably related to the intake of shellfish and travel to endemic areas. Approximately 60% of cases of symptomatic hepatitis B infection were acute exacerbations of chronic infection. Sexual exposure was the single most important risk factor for acute hepatitis B infection. The rarity of acute hepatitis C and D might be related to the low rate of intravenous drug use in our locality. Hepatitis E virus probably contributed significantly to the cases of non-ABC hepatitis. Further studies are needed to establish the importance of various causative agents of acute hepatitis in Hong Kong.