A prospective study of infants born to women with diabetes mellitus is reported. The children were examined at birth and followed at 1, 3, and 5 years of age. Medical and psychological information was obtained through follow-up examinations. Intrauterine growth was atypical and there was an increase in neonatal problems and congenital malformations. There was an increased incidence of intellectual delay at 3 and 5 years of age. The presence of acetone in the urine during pregnancy had a significant, adverse effect on intellectual status of the offspring at 5 years of age. Birth weight was negatively related to intellectual status at both 3 and 5 years of age.