Background: An external locus of control is associated with poorer psychopathology in individualist cultures, but associations are reported to be weaker in collectivist cultures where an external style is less maladaptive. We investigated the prospective association between externality and psychotic-like experiences and depressive symptoms and compared the strength of associations between a UK and a Japanese cohort.Method: Cross-cultural cohort study of a UK and a Japanese cohort. Externality was assessed using the Children's Nowicki and Strickland Internal, External Scale and DS (...) using the Short Moods and Feelings Questionnaire in both cohorts, PLE were assessed with the Psychosis-Like Experiences Questionnaire, and the Adolescent Psychotic-Like Symptom Screener. Associations were investigated using multivariable regression models and bivariate regression models to compare the strength of associations.Results: Mean externality in both childhood and adolescence was higher in ALSPAC than in the TTC. Childhood externality was associated with PLE in late childhood and adolescence in both cohorts and adolescent externality was associated with PLE in young adulthood in the ALSPAC cohort. There was a more mixed pattern of association between externality and DS scores. There was little evidence of any differences in the strength of associations between externality and different psychopathologies, or between cohorts. In ALSPAC adolescent externality and early adult psychopathology were more strongly associated than childhood externality and adolescent and early adult psychopathology. There was no evidence that change in externality between childhood and adolescence was associated with new onset PLE or DS in early adulthood.Conclusion: An external locus of control is associated with poor mental health regardless of cultural context. (shrink)