The clinical and evolutive characteristics and the response to treatment of a series of 49 patients with autoimmune hepatitis (AIH) diagnosed in the Liver Unit of a tertiary hospital from 1979 to 1996 and followed over 5.6 +/- 0.7 years were reviewed. Forty cases (80.4%) were AIH type 1 (ANA/AML positive), 7 (14%) type 2 (ALKM positive) and 2 (5%) of an undetermined type (absence of detectable antibodies). In 13 (26.6%) the disease presented as acute hepatitis and 16 (32%) presented extrahepatic manifestations. The AIH type 2 was observed in younger patients with the debut being more acute than in AIH type 1, but no significant differences were observed between the two groups with regard to the results of laboratory tests, frequency of a systemic manifestations and histologic lesions. Immunosuppressive treatment was effective in 90% of the cases, but 11 (30%) out of 37 relapsed on suppression of prednisone or reduction of the dosis. All showed response on reinitiation or an increase in the dosis of prednisone. Progression to cirrhosis was observed in 17% of the patients without cirrhosis at the time of diagnosis despite biochemical remission induced by treatment. No patient died during the follow up but 4 required liver transplantation.