INTRODUCTION. Socio-economic position (SEP) is a powerful source of health inequality. Less is known of early life conditions that may determine the course of adult SEP. We tested if early life stress (ELS) due to a separation from the parents during World War II predicts adult SEP, trajectories of incomes across the entire working career, and inter-generational social mobility. MATERIALS AND METHODS. Participants (n = 10,702) were from the Helsinki Birth Cohort Study 1934-44. Compared to the non-separated, the separated individuals attained a lower SEP in adulthood. The separated whose fathers were manual workers were less likely to be upwardly mobile from paternal occupation category to higher categories of own occupation, education, and incomes. The separated whose fathers had junior and senior clerical occupations were more likely to be downwardly mobile. Comparison of trajectories of incomes across adulthood showed that the difference between the separated and the non-separated grew larger across time, such that among the separated the incomes decreased. CONCLUSIONS. This life-course study shows that severe ELS due to a separation from parents in childhood is associated with socio-economic disadvantage in adult life. Even high initial SEP in childhood may not protect from the negative effects of ELS.