A previously well young woman presented with an acute hepatitis resembling viral hepatitis and a liver biopsy after 5 weeks showed features of acute hepatitis. Infection with identifiable viruses or other organisms known to cause hepatitis was excluded. Evidence for autoimmune chronic active hepatitis ab initio included prolonged fever, lymphadenopathy, urticaria, arthralgia, Coombs' positive hemolytic anemia, lymphopenia, a markedly raised level of immunoglobulin G and a positive antinuclear antibody test. Liver biopsies after 4 and 28 months showed typical histologic features of autoimmune chronic active hepatitis and the subsequent clinical course was typical, being marked by relapses and remissions responsive to prednisolone. Thus, described here is a woman in whom an acute onset of autoimmune chronic active hepatitis was clinically and histologically identified.