Substance abuse by pregnant women continues to be one of the leading problems in modern obstetrics. The frequency of abuse of more than one substance, especially with alcohol and tobacco, makes interpretation of the literature difficult; however, there is little doubt that substance abuse is associated with poor pregnancy outcome. Furthermore, abstinence and prenatal care are associated with improved perinatal outcomes. Despite the positive impact of perinatal care, however, continued abuse of substances during pregnancy can result in infant impairment. Clinicians who provide care to pregnant women should be alert to the possibility of substance abuse in all women so that treatment can be offered and complications can be anticipated, or better, avoided. At the time of the first prenatal visit, all pregnant women should be questioned thoroughly about past and present drug use. While toxicology screening may be helpful in some circumstances, universal screening is not recommended. Practitioners should be familiar with testing and reporting requirements in their state. Substance abusers should be counseled about the risks posed by continued substance use. At each prenatal and postpartum visit, substance abuse treatment should be offered to those who have not quit. When possible, it is helpful to work with a multidisciplinary team to address the various problems associated with substance abuse.