A number of studies have suggested that the clinical course of hepatitis A virus (HAV) infection is more severe in patients with chronic liver disease (CLD). A study was undertaken to determine the impact of acute HAV in asymptomatic hepatitis B surface antigen (HBsAg) carriers (n = 20) and patients with hepatitis B virus (HBV)-(n = 8) or hepatitis C virus (HCV)-related (n = 4) CLD. Disease progression was compared with that in 100 patients with isolated HAV infection. No patient with HAV infection alone developed complications, and all recovered fully. Fulminant or submassive hepatitis occurred in 55% of HBsAg carriers and 33% of patients with HBV- or HCV-related CLD. The mortality rate in HBsAg carriers (25%) was not significantly different from that in the patients with CLD (33%). The seroprevalence of anti-HAV immunoglobulin G in 820 individuals was also determined. Approximately 50% of the individuals had acquired HAV infection between the ages of 21 and 30 years. It was demonstrated that HAV infection may have a more severe clinical course in patients with underlying CLD, particularly among older individuals. Vaccination for such patients should be considered.