Using a prospective design, this study examined (a) whether hyperactive children suffer from low self-esteem as adolescents; (b) whether low self-esteem is associated with poor functioning in adolescence; (c) whether hyperactive children exhibit a positive illusory bias, in which self-esteem is independent of level of functioning; and (d) whether self-esteem in adolescence is associated with poor functioning in adulthood. Subjects were 65 children diagnosed as hyperactive in childhood, and 62 matched controls sampled from a medical clinic. After controlling for current mental disorder, the hyperactive cohort reported lower self-esteem in adolescence, was judged by clinicians to have lower levels of overall adjustment in adolescence, and had lower educational achievement and occupational rank in adulthood, as compared to controls.