In this longitudinal study, the bidirectional relations between parenting and friends' deviance, on one hand, and early adolescent externalizing and internalizing problem behavior, on the other hand, are examined. Of the 650 adolescents (13- to 14-year-olds) who filled out the Youth Self-Report and questionnaires about their parents at two times within a 1-year interval, 141 adolescents could be paired, at both assessments, with the same best friend who also filled out the questionnaires. Stable friends were used as a control for selection effects within friendships. The results showed significant effects of adolescent externalizing and internalizing problem behavior on parenting 1 year later, but not vice versa. Friends' deviance affected adolescent externalizing but not internalizing problem behavior over time. The inclusion of friends' self-reports about their own behavior and the examination of reciprocal effects seems to be a step forward in understanding the processes among parents, peers, and early adolescent problem behavior. (Contains 2 tables and 2 figures.)