Background: Previous studies have shown that adolescent mental health problems are associated with lower employment probabilities and risk of unemployment. The evidence on how earnings are affected is much weaker, and few have addressed whether any association reflects unobserved characteristics and whether the consequences of mental health problems vary across the earnings distribution., Methods: A population-based Norwegian health survey linked to administrative registry data (N=7885) was used to estimate how adolescents' mental health problems (separate indicators of internalising, conduct, and attention problems and total sum scores) affect earnings (≥30 years) in young adulthood. We used linear regression with fixed-effects models comparing either students within schools or siblings within families. Unconditional quantile regressions were used to explore differentials across the earnings distribution., Results: Mental health problems in adolescence reduce average earnings in adulthood, and associations are robust to control for observed family background and school fixed effects. For some, but not all mental health problems, associations are also robust in sibling fixed-effects models, where all stable family factors are controlled. Further, we found much larger earnings loss below the 25th centile., Conclusions: Adolescent mental health problems reduce adult earnings, especially among individuals in the lower tail of the earnings distribution. Preventing mental health problems in adolescence may increase future earnings., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.)