Discrepancies between children and partners (e.g., parents, friends, peers) in reports of social functioning and self-other relationships are common in clinical practice and in research. However, it is not clear whether children’s biased perceptions of self-other relationships, relative to the reports of partners, are predominantly a reflection of underlying psychological dysfunctions or whether these biased perceptions present a risk factor for subsequent problematic development. This longitudinal study therefore examined the effects of adolescent-mother disagreement and adolescent-best friend disagreement in perceptions of close (dyadic) relationships on the development of psychopathology in early adolescence. The sample included 497 thirteen year-old adolescents of Dutch-Caucasian backgrounds (57 % boys; 41 % at high risk for externalizing problems), their mothers, and self-nominated best friends. The participants completed reports of positive dyadic relationship quality (warmth) in Grade 7. Discrepancy scores were based on difference scores between the adolescents’ versus the partners’ reports. Both absolute disagreement and direction of disagreement (i.e., over- or underestimation relative to the relationship partner) were examined. Self-reported symptoms of depression and mother-reported aggression were assessed in Grade 7, 8, and 9. Absolute disagreement in perceptions of warmth between adolescents and best friends was significantly related to higher baseline levels of aggression. No significant effects of discrepancy scores on growth curves of symptoms of depression and aggression were found. The results may suggest that it is more important for adolescents to develop positive perceptions of close relationships than to agree with partners on the quality of the relationship.