The participants were born in 1972, 1974, 1976, 1978, and 1980. They and peers whom they suggested were interviewed in 1989 and 1990. The research used six measures of self-reported juvenile delinquency and juvenile drug use and a measure of perceived general delinquency of peers. Findings indicated that peer problem behavior measures, using either peer-self report measures or more indirect perceptual measures, were important in the understanding of problem behavior. Peer behavior, regardless of the measurement, was consistently the strongest predictor of the participant's problem behavior. In addition, the data suggested that both the actual behavior of peers and that behavior as perceived by an individual youth may be important predictors of involvement in problem behavior. This finding suggested the importance of the peer group for intervention strategies. It may also be important to help individuals understand that their perceptions of their friends' problem behavior may not be too accurate. In addition, program and treatment organizers need to be aware that peers serve both prosocial and antisocial functions, and that bringing delinquent youth together may be counterproductive. However, the data did not account for much of the variation in individual reports of behavior. These data are preliminary; further search is needed. Tables and 17 references