Although an estimated 1 million persons in the United States are chronically infected with hepatitis B virus, the prevalence of hepatitis B has declined since the implementation of a national vaccination program. Hepatitis B virus is transmitted in blood and secretions. Acute infection may cause nonspecific symptoms, such as fatigue, poor appetite, nausea, vomiting, abdominal pain, low-grade fever, jaundice, and dark urine; and clinical signs, such as hepatomegaly and splenomegaly. Fewer than 5 percent of adults acutely infected with hepatitis B virus progress to chronic infection. The diagnosis of hepatitis B virus infection requires the evaluation of the patient's blood for hepatitis B surface antigen, hepatitis B surface antibody, and hepatitis B core antibody. The goals of treatment for chronic hepatitis B virus infection are to reduce inflammation of the liver and to prevent complications by suppressing viral replication. Treatment options include pegylated interferon alfa-2a administered subcutaneously or oral antiviral agents (nucleotide reverse transcriptase inhibitors). Persons with chronic hepatitis B virus infection should be monitored for disease activity with liver enzyme tests and hepatitis B virus DNA levels; considered for liver biopsy; and entered into a surveillance program for hepatocellular carcinoma.