Autoimmune hepatitis is an unresolving, hepatocellular inflammation of unknown cause that is characterized by the presence of periportal hepatitis on histologic examination, tissue autoantibodies in serum, and hypergammaglobulinemia. By international consensus, the designation autoimmune hepatitis has replaced alternative terms for the condition. Three types of autoimmune hepatitis have been proposed based on immunoserologic findings. Type 1 autoimmune hepatitis is characterized by the presence of antinuclear antibodies (ANA) or smooth muscle antibodies (SMA) (or both) in serum. Seventy percent of patients with type 1 of autoimmune hepatitis are women. This type is the most common form and accounts for at least 80% of cases. Type 2 is characterized by the presence of antibodies to liver-kidney microsome type 1 (anti-LKM1) in serum. Patients with this type of autoimmune hepatitis are predominantly children. Type 3 autoimmune hepatitis is characterized by the presence of antibodies to soluble liver antigen (anti-SLA) in serum. There are no individual features that are pathognomonic of autoimmune hepatitis, and its diagnosis requires the confident exclusion of other conditions. The large majority of patients show satisfactory response to corticosteroid (usually prednisone or prednisolone) therapy. For the past 30 years it has been customary to add azathioprine as a "steroid sparing" agent to allow lower doses of steroids to be used and remission, once achieved, can be sustained in many patients with azathioprine alone after steroid withdrawal. Patients with autoimmune hepatitis who have decompensated during or after corticosteroid therapy are candidates for liver transplantation.