An estimated 350 million persons worldwide and 1.25 million in the United States are infected with hepatitis B virus (HBV). Hepatitis B carriers are at risk for development of cirrhosis and hepatocellular carcinoma (HCC). The natural history of chronicHBVinfection is variable. Persons with chronic HBV infection need lifelong monitoring to determine if and when intervention with antiviral therapy is needed and to observe for serious sequelae. These guidelines were developed under the auspices of, and approved by, the Practice Guidelines Committee of the American Association for the Study of Liver Diseases. The original guidelines were published in HEPATOLOGY 2001; 34: 1225–1241. In light of recent progress, particularly in the treatment of chronic hepatitis B, these guidelines were updated in September of 2003. A complete version of the updated guidelines, including a review of recently published literature, can be found at the AASLD web site, www.aasld.org. Following is a summary of the updated recommendations for treatment of chronic hepatitis B. The recommendations were graded as I (randomized controlled trials), II-1 (controlled trials without randomization), II-2 (cohort or case-control analytic studies), II-3 (multiple time series, dramatic uncontrolled experiments), and III (opinions of respected authorities, descriptive epidemiology).