The incidence, clinicopathologic features and etiology of acute exacerbation occurring in patients with liver cirrhosis were assessed prospectively among 332 hepatitis B surface antigen (HBsAg) positive and 71 HBsAg negative patients. During an 11-year period and a mean follow-up duration of 26.8 months, 148 acute exacerbation occurred in 107 HBsAg positive patients and 32 episodes occurred in 18 HBsAg negative patients. The calculated annual incidence was 11.5%. The clinical, laboratory and histologic features were similar to those in patients with chronic hepatitis. Confluent hepatic necrosis and alphafetoprotein elevation over 100 ng/ml occurred frequently, particularly in HBeAg positive patients. In general, acute exacerbations in HBsAg negative patients were less severe than their HBsAg positive counterparts. Of the exacerbations in HBsAg positive patients, 54.8% of the HBeAg positive ones and 38.6% of the HBeAg negative ones were attributable to hepatitis B virus reactivation, while 4.8% and 7.9%, respectively, were due to hepatitis delta virus superinfection. The others might be the results of hepatitis non-A, non-B virus superinfection or increased piecemeal necrosis. The immediate outcome of acute exacerbations in cirrhotic patients was usually good, although 13.8% developed hepatic decompensation and 4.4% died. Further follow-up study is required to evaluate the long-term effect of the frequent occurrence of bridging hepatic necrosis, high elevation of alphafetoprotein and hepatic decompensation during acute exacerbation in cirrhotic patients.