PurposeGender differences in youth self-harm are sparsely studied regarding long-term prognoses. We aimed to study the gender differences in effects of adolescent self-harm in early adult life in four domains: 1/family situation, 2/education and employment, 3/mental illness and suicidal behaviour, and 4/suicide and all-cause mortality.MethodA register-based cohort study including all Swedish residents aged 20 during 2001–2005 was performed. Exposure was self-harm at ages 10–20, and outcomes were death and suicide and past-year records of self-harm, marital status/children, education/employment, and mental health at age 30. We used logistic regression for dichotomous outcomes, and Cox regression models for time-dependent outcomes. An interaction term was introduced to detect significant gender effects, in which case we performed stratified analyses.ResultsSubjects with self-harm before age 20 had a poorer prognosis for all studied outcomes, and risk estimates were similar for men and women for most outcomes including suicide. Significant interaction terms (ITs) were found, revealing gender differences, for being married (pIT 0.0003; ORmen 0.6, ORwomen 0.9), being a parent (pIT < 0.0001; ORmen 0.7, ORwomen 1.1), receiving unemployment support (pIT < 0.0001; ORmen 2.4, ORwomen 1.8), and death from any cause (pIT 0.006; ORmen 10.6, ORwomen 7.4).ConclusionsAdolescent self-harm was associated with later life adversities and affected men more than women regarding prognoses for unemployment and certain aspects of the family situation. We found no gender difference for the effect of self-harm on the risk of suicide. Future suicide risk should not be underestimated in young self-harming women.