This study examined the effect of some maternal factors on the pre- and postnatal development of a group of infants of diabetic mothers (IDMs). Body weight, length and head circumference were measured at birth and at 3, 6, 12, 24, 36, and 48 months of age. No differences were observed in pre- and postterm growth when IDMs were subdivided according to the maternal White class or pregnancy complications. Poor metabolic control during pregnancy resulted in excessive and abnormal prenatal growth; the fetal weight increased progressively during the last 3 weeks of gestation, while little or no increase was observed in fetal length or the head circumference which at 37 weeks both were already higher than (length) or similar to (head circumference) those of normal babies at term. Children of mothers with poor metabolic control during pregnancy showed significantly higher values for weight and weight/height ratio in infancy than children of well controlled mothers. Female offspring contributed most to the differences.