Previous studies of type I autoimmune hepatitis (AIH) have been based on selected populations attending specialist liver units. We describe 41 patients with type I AIH from a stable population in South Wales sequentially diagnosed over an 11-year period. All were Caucasian; 32 women, nine men; median follow-up 4 years. All cases conformed with International AIH Group criteria. Median age at diagnosis was 62 years. At presentation, only five patients were under 40 years old, 23 were over 60. This was very different from the classical age distribution. The commonest presentation was acute icteric hepatitis (29/41); median duration of illness 3 months. Co-existing acute arthralgia was common (10/41), as were other autoimmune diseases. Liver biopsy revealed piecemeal necrosis or interface hepatitis in 30; others showed non-diagnostic acute hepatitis. Fourteen also had cirrhosis. Median AsT fell from 508 (73-2385) to 32 (13-607) U/I after immunosuppression, representing complete remission in 28, partial remission in eight, and two treatment failures. Three patients were not treated, because of either quiescent disease or spontaneous remission. To date, there have been eight deaths (median age 64, range 37-86); five due to liver failure, one to variceal haemorrhage, one to acute myocardial infarction and one to upper gastrointestinal haemorrhage caused by acute idiopathic thrombocytopenia. Contrary to previous descriptions, type 1 AIH is a disease of later life in this stable, unselected population; peak incidence was in the seventh decade, and few cases occurred before the fifth decade. Presentation was usually as painless acute icteric hepatitis. Immunosuppression was effective and safe in most cases; 5-year survival rates were 61% (> 60 years at diagnosis), 66% (< 60) and 64% (overall).