A relationship between parental substance abuse and subsequent alcohol problems in their children has been documented extensively. Children of alcoholics (COAs) are considered to be at high risk because there is a greater likelihood that they will develop alcoholism compared with a randomly selected child from the same community. COAs and children of other drug-abusing parents are especially vulnerable to the risk for maladaptive behavior because they have combinations of many risk factors present in their lives. The single most potent risk factor is their parent's substance-abusing behavior. This single risk factor can place children of substance abusers at biologic, psychologic, and environmental risk. Since the turn of the century, many reports have described the deleterious influence of parental alcoholism on their children. A series of studies measured mortality, physiology, and general health in the offspring of alcoholic parents and concluded that when mothers stopped drinking during gestation, their children were healthier. Today, research on COAs can be classified into studies of fetal alcohol syndrome, the transmission of alcoholism, psychobiologic markers of vulnerability, and psychosocial characteristics. Each of these studies hypothesizes that differences between COAs and children of nonalcoholics influence maladaptive behaviors later in life, such as academic failure or alcoholism. This research supports the belief that COAs are at risk for a variety of problems that may include behavioral, psychologic, cognitive, or neuropsychologic deficits. The vast literature on COAs far outweighs the literature on children of other drug abusers. Relatively little is known about children of heroin addicts, cocaine abusers, or polydrug abusers. Nonetheless, many researchers suggest that the children of addicted parents are at greater risk for later dysfunctional behaviors and that they, too, deserve significant attention to prevent intergenerational transmission of drug abuse. Most research on children of other drug abusers examines fetal exposure to maternal drug abuse. The overview of the research on children of substance abusers points toward the need for better, longitudinal research in this area. Most studies on COAs or other drug abusers are not longitudinal; they examine behavior at one point in time. Given the studies reviewed in this article, it is unclear whether we see true deficits or developmental delay. Longitudinal studies will allow us to predict when early disorders and behavioral deviations will be transient or when they will be precursors to more severe types of maladaptive behavior. Longitudinal research also will enable us to explain specific childhood outcomes. Differences in outcome could be studied simultaneously to understand whether antecedents discovered for one are specific to it or are general antecedents leading to a broad variety of outcomes.