The sample consisted of 138 male and 105 female adolescents who were recruited at a hospital-based adolescent drug-abuse treatment program. They were administered assessments with the PEI Psychosocial scales at intake, discharge, and 6 and 12 months after discharge. The PEI is a 276-item paper-and-pencil multiple scale, self-administered questionnaire that measures adolescent drug-abuse problem severity and several psychosocial factors related to problem severity. This study focused on the main clinical scale of the PEI, i.e., Personal Involvement with Chemicals, as a measure of outcome, along with all 12 of the PEI Psychosocial scales as predictor variables. The Psychosocial scales measure negative self-image, psychological disturbance, social isolation, uncontrolled behavior, rejection of convention, deviant behavior, absence of goals, spiritual isolation, peer chemical environment, sibling chemical use, family pathology, and family estrangement. The study found that intake PEI Psychosocial scales were modestly predictive of treatment outcome, and the magnitude of the predictions were higher for boys than girls. The PEI Psychosocial domains of deviance, family dysfunction, and peer drug use were predictive of boys' outcome, and sibling and peer drug use were predictive of girls' outcome. The strength of these predictive relationships was similar to those found in other treatment outcome prediction research. Thus, there was limited support for the predictive validity of the PEI. The PEI Psychosocial scales that have predictive associations with outcome may be useful in treatment planning. 6 tables and 41 references