Autoimmune hepatitis is a generally progressive, chronic disease with occasionally fluctuating activity that occurs worldwide in children and adults. Although the cause of autoimmune hepatitis is unknown, aberrant autoreactivity is thought to have a role in its pathogenesis. The diagnosis is based on histologic changes, characteristic clinical and biochemical findings, circulating autoantibodies, and abnormal levels of serum globulins. Variant forms of autoimmune hepatitis share features with other putative autoimmune liver diseases, primary biliary cirrhosis, and primary sclerosing cholangitis. Despite its clinical heterogeneity, autoimmune hepatitis generally responds to antiinflammatory or immunosuppressive treatment, or both. Lifetime maintenance therapy may be required, especially for patients with type 2 autoimmune hepatitis and those who have cirrhosis at presentation. Liver transplantation has been successful in patients who have no response to medical management. Copyright © 2006 Massachusetts Medical Society.