Birth out of wedlock has been associated with maternal and neonatal problems, especially low birthweight, attributed mainly to the young maternal age of the unmarried mothers. We surveyed a cohort of 300 first-born infants delivered in Israel to unwed mothers, matched for parity, maternal age, and ethnic origin. No maternal complications were found among the unwed mothers. However, the incidence of intrauterine growth retardation among infants of the out of wedlock mothers was 53 of 293, compared with 20 of 297 among the control population (p less than 0.001). This difference in the incidence of intrauterine growth retardation may not be associated with young maternal age.