The study hypothesized that the quality of the interpersonal relationships with parents and peers would predict individual differences in changes in internalizing and externalizing problems for both boys and girls, but the strength of these associations would be greater for girls than for boys. The study used three measurement waves at 1-year intervals. The sample consisted of 212 adolescents (100 boys and 112 girls) with mean age of 13.4 years at the time of the initial assessment. Only four adolescents did not have data on all three waves. At each wave, the families were visited at their homes by trained interviewers. During the visits, adolescents completed a battery of questionnaires that measured problem behavior, the quality of the adolescent-parent relationship, and the quality of the adolescent-peers relationship. The findings showed substantial absolute and relative stability in both internalizing and externalizing problem behavior; however, there were significant individual differences in both initial levels of problem behavior and in the rate of change across the three measurements. Adolescent gender and the quality of the parent-adolescent relationship predicted the initial level of both types of problem behavior. A warm, intimate relationship with parents tended to function as a protective factor against both internalizing and externalizing problem behavior. Positive relationships with peers provided a protective effect for internalizing but not for externalizing problem behaviors. Adolescents who reported poor communication and lack of trust and intimacy in peer relations experienced more depressive moods and a higher rate of growth in these problems than adolescents who had positive peer relations. There were no apparent differences between boys and girls regarding the effect of the quality of interpersonal relations on the level and the range of change in problem behavior. This suggests that the etiology of problem behavior might be similar for boys and girls even though there were gender differences in the prevalence of problem behaviors. 3 figures, 2 tables, and 72 references