This article summarizes what is known about the effects of cocaine, opiates, marijuana, and alcohol on neonatal and postnatal growth and development. The development of a child affected by prenatal exposure to drugs and alcohol is best understood through a multifactorial model consisting of interrelated prenatal and postnatal factors. The article also describes the prenatal effects of drugs and alcohol on the newborn, especially on central nervous system functioning, which is seen as creating a biologic vulnerability that renders a child more vulnerable to the effects of poor caretaking.