Three hundred children chosen at random from the general population were examined at 9 years of age and seen again at 20. The results of the study emphasize the discontinuity of psychological problems between childhood and adulthood: serious difficulties in psychological functioning at age 9 do not predict disturbances at 20, but psychological disturbances at 20 may originate in adolescence. The overrepresentation, at age 9, of boys at risk disappears at 20, at which point there is a slightly higher proportion of women amongst the "cases". The factors which influence the mental health of girls and boys are analysed and discussed.