The sample included 579 youths in secondary schools and 390 incarcerated juvenile delinquents. The youths completed self-report questionnaires. Data were collected from November 1993 to February 1994. Results revealed high rates of drug use, because a large part of the sample consisted of institutionalized offenders. The sample included 151 regular heroin users who took the drug more than once a day. All but two of the heroin users were incarcerated. Drug use frequencies were highly asociated with psychosocial variables such as peer drug use, family drug use, susceptibility to peer pressure, perceived control to gain access to drugs, and perceived adverse consequences of drug use. The correlations between perceived peer drug use and marijuana use were 0.59 for males and 0.73 for females. Findings underscored drug use among adolescents as typically a social behavior that is developed and maintained in deviant peer groups. Tables and 3 references