Objective To analyze and compare the clinical manifestations,biological and chemical indices,immunological indices,and liver biopsy histological features of autoimmune hepatitis(AIH) according to patient age.Methods Ninety-eight adult Chinese patients diagnosed with AIH were divided into three groups according to age:<45 years="" 45-60="" and="">60 years old(elderly).Significance of inter-group differences in the clinical manifestations,biological and chemical indices,immunological indices,and liver biopsy histology was assessed by ANOVA(normally distributed data) or Wilcoxon rank test(non-normally distributed data).Results The elderly patients had a significantly higher frequency of hepatopathy than the young patients(50% vs.20%,P<0.05) and a higher frequency of cirrhosis than either the young patients(40.6% vs.5.7%,P<0.05).The elderly patients also had higher levels of total bilirubin(TBil) than the young patients(P<0.05).The level of serum complement factor 4(C4) was remarkably lower in the middle-aged patients and elderly patients than in the young patients(P<0.05).The elderly patients had a higher frequency of antinuclear autoantibodies(ANA) positivity but lower frequency of anti-smooth muscle autoantibodies(SMA) positivity than the young patients(ANA:100% vs.77.1%,P<0.05;SMA:31.4% vs.6.3%,P<0.05).The middle-aged and elderly patients had higher frequencies of interface hepatitis than the young patients(88.5% and 100% vs.51.8%,P<0.05).The histology activity index(HAI) was also remarkably higher in the middle-aged and elderly patients than in the young patients(8.1±2.8 and 10.2±3.6 vs.6.6±2.3,P<0.05).Conclusion Elderly AIH patients have higher frequencies of cirrhosis and complications,as well as stronger inflammatory activities.