The relationship between maternal birth weight and infant birth weight was studied in the Buffalo cohort of the Collaborative Perinatal Project (n = 1,348). Regression techniques were used to control for confounders. Compared with infants of mothers who had weighed 8 lb or more at birth, infants of mothers who had weighed 6 to 7.9 lb, 4 to 5.9 lb, and less than 4 lb at birth were 99 g, 244 g, and 170 g lighter, respectively. The adjusted odds ratios of giving birth to an infant of birth weight less than 2,500 g, with mothers of birth weight 8 lb or more as the reference group, were 3.46 and 1.66 for mothers of birth weight 4 to 5.9 lb and 6 to 7.9 lb, respectively. There were no infants less than 2,500 g among the 24 women who had weighed less than 4 lb at birth. These data suggest a possible role of genetic and familial factors in determining birth weight.