Recent studies, particularly those in Orientals, have shown that both acute exacerbation from the reactivation of the original virus and acute superinfection with other viruses occur frequently in patients with chronic viral hepatitis. The clinicopathologic features of acute exacerbation and acute superinfection are similar to those of acute hepatitis caused by a single virus, but acute exacerbation is usually less severe than acute superinfection. Recurrent acute exacerbations result from the host's intermittent but persistant efforts to eliminate the replicating virus by immune-mediated mechanisms, thus killing hepatocytes with viral replication. Severe acute exacerbation or acute superinfection may result in immediate hepatic decompensation, or even mortality, and late disease progression, including liver cirrhosis and hepatocellular carcinoma. Further studies are needed to elucidate the basic mechanisms and provide more effective ways to avoid acute exacerbation and acute superinfection in patients with chronic viral hepatitis.