The prevalence of both hepatitis A and hepatitis B is increased in homosexual men. On an annual basis, 5% to 7% of homosexual men will acquire hepatitis A. Risk factors for HAV infection include length of homosexual activity, number of sexual contacts, and oral--anal sexual contact. The HBsAg carrier rate of homosexual men is 5% to 6%, and another 50% have evidence of previous HBV infection with a positive anti-HBs. HBeAg is present in a higher precentage of HBsAg-positive homosexual men (38% to 75%) than in general population carriers (3% to 30%). The annual incidence for HBV infection in homosexual men is 16% to 28%, higher than that for hepatitis A. Transmission of HBV infection in homosexual men is facilitated by a large number of sexual partners, high HBsAg carrier rate, high infectivity of carriers (positive HBeAg), and the specific sexual practices of oral--anal and anal--genital contact with exposure to HBV on open mucosal surfaces. The prevalence of non-A, non-B and delta infection in homosexual men is probably somewhat increased, but the importance of these viruses in the development of hepatitis in this population remains uncertain. Prevention of hepatitis A and B in homosexual men will ultimately be achieved by vaccination of susceptible individuals, which currently is feasible only for hepatitis B. Appropriate use of immune globulins for postexposure prophylaxis and knowledge of specific sexual practices that transmit disease may reduce the incidence of hepatitis A and B.