Little is known about the long-term consequences of positive well-being in childhood in the general population. We analysed data from the British 1946 birth cohort study to test associations between adolescent positive wellbeing and well-being in midlife. Positive and negative behaviours at ages 13 and 15 were rated by school teachers, and personality was assessed when the children were 16 years. Positive childhood behaviour was associated with midlife well-being; specifically a low probability of lifetime emotional problems, satisfaction with work, a high frequency of contact with friends or family and engagement in social activities. Happy children in this cohort were no more likely to marry, but significantly more likely to divorce. These associations were independent of childhood social class, childhood cognition, educational attainment, midlife occupational social class and extraversion. From this longitudinal study, we conclude that childhood well-being predicts positive adult wellbeing, and not merely the absence of mental ill-health.