Substance abuse in pregnancy is a major area of interest for clinicians, researchers, and public health officials. Cigarettes have long been associated with poor reproductive outcomes. Smoking increases the relative risk of placenta previa to 2.6 and of sudden infant death syndrome to 2.2 in white infants. The risk-to-benefit ratio of nicotine replacement therapy is discussed. Alcohol use by pregnant women decreased from 32% to 20% between 1985 and 1988. The long-term sequelae of fetal alcohol syndrome in adolescents and adults are presented. Marijuana is probably the most common illicit drug used in pregnancy. Long-term follow-up showed no difference in outcome until 48 months. However, at 48 months, memory and verbal measures were affected by heavy prenatal marijuana use. Self-report of illicit drug use is inaccurate. Routine urine screening for cocaine can show marked variations by locality. Analysis of meconium, urine, and infant and maternal hair along with self-report provides the most accurate information on prenatal cocaine use. The increase in cost of caring for cocaine-exposed infants was estimated. Newborns reveal decreased habituation and increased neonatal stress measures. Long-term sequelae of prenatal cocaine use indicated that smaller head circumference persists and that head size is associated with Bayley mental developmental indexes. However, the Bayley scale measured no difference among the cocaine-exposed, alcohol-exposed, or control groups.