This article includes a summary and critique of methodological limitations of the peer-reviewed studies of developmental outcome during the first 2 years in children prenatally exposed to the most commonly used drugs of abuse: tobacco, alcohol, marijuana, heroin/methadone, and cocaine. Reported effects vary by specific drug or drug combinations and amount and timing of exposure; however, few thresholds have been established. Drug effects also appear to be exacerbated in children with multiple risks, including poverty, and nonoptimal caregiving environments. Although prenatal exposure to any one drug cannot reliably predict the outcome of an individual child, it may be a marker for an array of variables that can impact development. Appropriate intervention strategies require future research that determines which factors place exposed children at risk and which are protective for optimal development.