Findings show that although the girls may have begun substance use at earlier ages than boys, there were few differences in the frequency of substance use. Girls reported a slightly greater level of current hard-drug use, but the means for current alcohol/marijuana use were almost identical for girls and boys. Peer substance use was a significant factor in substance use for both genders. Youth who were more peer-oriented than parent-oriented were at higher risk for substance use and other forms of problem behavior. Gang involvement was significantly associated only with age of first alcohol/marijuana use, and only among boys. Family variables as a whole performed better as predictors of age at first alcohol/marijuana use than for any of the other substance-abuse variables. The findings were more consistent with the tenets of differential association/social learning theory (the significant influence of substance-using peers and being allowed to drink at home) than those of general strain theory, which suggests that delinquency results from a youth's emotional response to negative relationships with others that leads to failure to obtain a valued goal. The study obtained data on all youth committed to Virginia's Department of Juvenile Justice between July 1, 1998, and June 30, 2003 (4,846 boys and 576 girls). The portion of the Adolescent Problem Severity Index (APSI) that focuses on alcohol and illicit substance use provided data for the dependent variables. The APSI was administered to committed youth at intake. Independent variables pertained to the youths' families, living situations, victimization experiences, and peer influences. 5 tables, 94 references, and appended variables and coding