This cross-sectional study explores potential mediating effects of parental monitoring of peers on three adolescent problem behaviors (externalizing behavior, drug use, sexual risk behavior) among juvenile delinquents and their families. Participants are 190 African American and Hispanic adolescents and parent guardians enrolled in a family therapy treatment efficacy study targeting delinquency. Parental monitoring of peers mediates the association between family functioning and externalizing behavior in the full sample. Comparable results are not found in post hoc analyses of each racial and ethnic sample or among drug use and sexual risk behaviors. Research and health service implications are discussed. (Contains 3 tables and 2 figures.)