Since early weaning in infancy has been known to result in vulnerability to infection, weaning times of 145 children diagnosed as autistic by DSM-III were statistically compared with those of 224 normal children in the same catchment area: 24.8% of the patients and 7.5% of the controls were weaned by the end of 1 week, a significant difference. Early weaning because of the mother's rather than the child's condition occurred with 17.9% of the patients and 5.8% of the controls, also a significant difference. Historical studies on infantile autism revealed that the disease developed more prevalently in the socioeconomic status where the incidence of breast-feeding was less frequent. These results suggest that early weaning may contribute to the etiology of infantile autism.