ObjectiveTo identify risk factors for preadolescent onset suicidal behavior compared with adolescent/young adult onset suicidal behavior in a longitudinal sample of youth with parental history of mood disorders. MethodsThe sample includes 545 youth who were age 21 years or less at the time of their baseline assessment. Participants underwent baseline and yearly study assessments. Observations were censored at the time point closest to the first episode of suicidal behavior for youth with suicidal behavior and at the time of last observation for youth without suicidal behavior. Youth were categorized into 3 groups: first onset of suicidal behavior before the age of 13 (n = 32), first onset of suicidal behavior between the ages of 13–21 (n = 51) and those without suicide related behaviors (n = 462). ANOVA, Chi-square, Fisher’s exact test and multinomial regression were used to test the hypotheses. ResultsSignificant predictors of preadolescent onset suicidal behavior were diagnosis of depressive disorder (RRR = 11.41, p<.001) and diagnosis of ADHD (RRR = 2.86, p = .02). Adolescent onset was predicted by diagnosis of depressive disorder (RRR = 4.12, p = .008), female sex (RRR = 2.68, p = .02) and self-reported suicidal ideation (RRR = 1.48, p = .004). LimitationsThese results are most applicable to offspring of parents with significant mood disorders. ConclusionsThe strongest predictor of suicidal behavior in both groups was a diagnosis of depressive disorder, and the risk was nearly 3 times higher in preadolescents. ADHD was a significant predictor only for preadolescents, while female sex and self-reported suicidal ideation predicted suicidal behavior in adolescents.