【Objective】 To explore the differences of perinatal risk factors and relative family history between autism and mental retardation. 【Methods】 A case-control study carried out on three groups:100 autistic patients,60 mental retardation patients and 80 healthy controls with normal development.Patients and controls in the three groups were recruited from Children's Hospital of Fudan University.ANOVA,Rank-sum test and Chi-square test methods for statistical analyses were used . 【Results】 Both patient groups with autism and mental retardation had a significantly higher rate of family history (35.0% vs 6.3%,P＜0.001;31.7% vs 6.3%,P=0.005)than control group.However,there was no statistical significance between the two patient groups (P=0.362).The rates of maternal conditions during pregnancy were different between three groups (28.00% vs 45.00% vs 26.25%,χ²=6.635,P=0.036),but there was no statistically significant difference between every pairs of groups in pairwise comparison.Maternal age in autistic group was significantly higher than that of control group (P＜0.001).With respect to perinatal history of hypoxia or asphyxia,no significant difference was observed between the three groups,neither were No.of previous pregnancies and deliveries,gestational age at birth,mode of delivery and birth weight. 【Conclusions】 1)Patients with autism and mental retardation have a similar rate of family history,and both are significantly higher than the normal children;2)Late pregnancy may be a risk factor for autistic disorder.