The incidence and characteristics of AIH differ in various geographic regions. Based on limited epidemiologic studies, the incidence of type 1 AIH among Caucasoid populations of Europe and North America ranges from 0.1 to 1.9/100,000/year. The disease is considerably less frequent in Japan. The relative proportion of AIH among cases with chronic hepatitis is low in regions with a high prevalence of viral hepatitis. Type 2 AIH is more frequent in southern Europe than in northern Europe, the United States, and Japan. The occurrence of anti-SLA/LP is also higher in European than in Japanese patients with type 1 AIH. The frequency of HLA markers that affect susceptibility to AIH varies between ethnic groups. DRB1*0301 (DR3) and DRB1*0401 (DR4) are the major risk factors for type 1 AIH in white European and North American populations. DRB1*0405 (DR4) is the principal risk factor in Japanese and adult Argentine patients with type 1 AIH, and DRB1*0404 (DR4) is the main susceptibility allele in Mestizo Mexicans. Children may have different clinical manifestations than adults, and the diagnoses of type 2 AIH, autoimmune sclerosing cholangitis, and APS1 should be considered. Uniform application of diagnostic criteria formulated by the International Autoimmune Hepatitis Group should strengthen future epidemiologic studies and extend awareness of AIH to yet unstudied minority groups.