Heroin abuse during pregnancy is associated with 1) fetal growth retardation and neonatal withdrawal syndrome in infants and 2) an increased frequency of abruptio placentae, sexually transmitted diseases, and other complications in mothers. Based on the findings of several small cohort studies, postnatal growth and development of infants whose mothers were addicted to heroin during pregnancy appears to fall within normal variation. In the present study, information about use of heroin and other substances during pregnancy in relation to neonatal outcome was analyzed in 47 heroin-abusing mothers and 80 control women and their respective infants. In addition medical record information was available for postnatal growth follow-up of 28 (58%) of heroin-exposed children and 22 (27.5%) of control infants. Infants born to heroin addicts in this study were significantly (P<.01) smaller at birth but exhibited no increase in the frequency of congenital anomalies compared with controls. Similar to findings of previous investigators, postnatal development of infants born to addicts was not delayed.