Objective: To assess the value of maternal and self-ratings of adolescent depression by investigating the extent to which these reports predicted a range of mental health and functional outcomes 4 years later. The potential influence of mother's own depressed mood on her ratings of adolescent depression and suicidal ideation on adolescent outcome was also tested. Method: A longitudinal population-based study of 842 adolescents ages 11 to 16 at the baseline assessment and 15 to 20 at follow-up (62% retention). Results: Both mother- and adolescent-rated depressive symptoms predicted future depression, antisocial behavior, impairment, health service use, and regular tobacco use in the adolescent. The odds ratios obtained for maternal and adolescent ratings of depressive symptoms as predictors of future psychopathology were not significantly different. Mothers' own depressive symptoms were not significantly associated with adolescent depression, health service use, or substance use at follow-up. Depression that was accompanied by adolescent-rated suicidal thoughts was significantly more strongly associated with impairment at follow-up than depression alone. Conclusions: It is possible to obtain clinically useful information on adolescent depression from the child's mother. However, information on suicidal ideation was rarely endorsed by mothers, suggesting that maternal report of adolescent suicidal thoughts shows less sensitivity than adolescent report. (Contains 4 tables.) [Funding for this study was provided in part by the Medical Research Council UK, the PPP Foundation, and the European Research Advisory Panel.]