The most extensive and consistent data related to youths' drug use pertained to their family interactions. The key predictors of youths' drug use were type and extent of parental discipline, family cohesion, and parental monitoring. Other family factors related to youths' drug use were large family size and having relatively young parents. There was extensive evidence that linked youths' drug use to parental substance use. Peer drug use and drug availability were consistently linked to adolescent drug use. Evidence was inconsistent in linking youths' drug use to factors in the following domains: mental health, attention deficit hyperactivity disorder, stimulant therapy, religious involvement, sports, health education, school performance, and socioeconomic status. For some of these categories, there was evidence of indirect effects on drug use. A relatively small body of research focused on factors related to youths' resistance to drug use in the face of constant exposure to known risk factors. Protective factors were social skills, positive social attachments, and material resources. A systematic search of electronic databases identified 251 relevant studies of adequate quality. Of these, 78 were randomly selected for further analysis. The analysis addressed methodology, type and level of drug use, type of data analysis, and the strength of relationships between predictive factors and drug use. 392 references