Autoimmune hepatitis is classically a disease of young women.Our aims were to determine its occurrence,clinical phenotype,and outcome in elderly patients and contrast findings to young adults.Two-hundred-and-five white North American adults with definite type 1 autoimmune hepatitis were grouped according to age at presentation and the groups compared.Forty-seven patients(23%)were aged≥60 years(median age,68 years),and 31 patients(15%)were aged ≤30 years(median age,25 years).The patients ≥60 years had a higher frequency of cirrhosis at presentation than the patients ≤30 years(33%versus 10%,P =.03).They also had thyroid or rheumatic diseases more commonly(42%vs.13%,P =.006).HLA DR3 occurred more frequently in the patients ≤30 years than in those ≥60 years(58%vs.23%,P =.004),and HLA DR4 occurred more often in the patients≥60 years(47%vs.13%,P =.003).Patients aged ≥60 years failed corticosteroid treatment less commonly than those aged ≤30 years(5%vs.24%,P =.03).Autoimmune hepatitis occurred in patients aged 18-30 years(15%),31-39 years(15%),40-49 years(21%),50-59 years(25%),and ≥60 years(23%).Differences in age distribution,HLA frequencies,and treatment outcome occurred after age ≥40 years.In conclusion,elderly patients have a greater frequency of cirrhosis at presentation and HLA DR4 than patients ≤30 years,and they have a lower occurrence of treatment failure.Transitions in clinical and genetic phenotypes occur after age ≥40 years.Genetic susceptibilities may favor etiologic factors that are age-related. Of those who were determined to have its occurrence, clinical phenotype, and outcome in elderly patients and contrast findings to young adults. Two-hundred-and-five white North American adults with definite type 1 autoimmune hepatitis were grouped according to age at presentation and the groups compared. Forty-seven patients (23%) were aged> 60 years (median age, 68 years), and 31 patients (15%) were aged <30 years years). The patient ≥60 years had a higher frequency of cirrhosis at presentation than the patients ≤30 years (33% versus 10%, P = .03) .they also had thyroid or rheumatic diseases more commonly (42% vs.13 %, P = .006) .HLA DR3 occurred more frequently in the patients ≤30 years than in those ≥60 years (58% vs.23%, P = .004), and HLA DR4 occurred more often in the patients ≥60 years (47% vs.13%, P = .003). Patients aged ≥60 years failed corticosteroid treatment less commonly than those aged ≤30 years (5% vs.24%, P = .03). Autoimmune (35%), 31-39 years (15%), 40-49 years (21%), 50-59 years (25%), and ≥ 60 years (23%). Differences in age distribution, HLA frequencies, and treatment outcome occurred after age ≥ 40 years. Conclusion, elderly patients have a greater frequency of cirrhosis at presentation and HLA DR4 than patients ≤ 30 years, and they have a lower occurrence of treatment failure. Transitions in clinical and genetic phenotypes occur after age ≥ 40 years. Genetic susceptibilities may favor etiologic factors that are age-related.