Although adoption has been viewed as a risk factor for mental disorders in children and adolescents, few studies have investigated this association in adults. To address this question, we analyzed data from a random community sample of adults where the presence of adoption in the first year of life was systematically noted and where the presence of lifetime mental disorders was determined by structured interview. In comparison to individuals raised by both biological parents, adoption was strongly associated with a history of childhood conduct disorder, antisocial personality and drug abuse or dependence. Adoption may thus be a risk factor for these mental disorders.