The association of fetal growth retardation with prenatal exposure to alcohol, smoking, opiates, and cocaine is well documented, but relatively little is known about the effects of these exposures on postpartum growth. This study assessed physical growth from birth through 6.5 and 13 months in 412 black, inner-city infants recruited on the basis of their mothers' use of alcohol and/or cocaine during pregnancy. Prenatal alcohol exposure was associated with a slower rate of growth during the first 6.5 postpartum months. This postnatal growth retardation was associated with maternal drinking during a critical period--the latter part of gestation--and was not related to drinking at the time of conception or to postnatal exposure to alcohol from breast-feeding. By contrast, smoking and cocaine use during pregnancy were associated with faster postnatal weight gain. Although maternal smoking was correlated with shorter stature at 6.5 and 13 months, this effect was attributable to maternal drinking during pregnancy, suggesting that the association of maternal smoking with shorter childhood stature reported elsewhere may be due to prenatal alcohol exposure, which was not controlled in prior studies.