Background: Childhood socioeconomic circumstances and childhood adversities influence body mass index (BMI) in young adulthood, but it remains unclear whether these influences persists in old age. Moreover, it is still unknown whether social mobility and adulthood socioeconomic circumstances mediate this association. Objectives: The objectives of this study are to examine if (1) childhood socioeconomic circumstances and childhood adversities are associated with trajectories of BMI in old age, and if (2) these associations are mediated by social mobility and ASC. Methods: Using a sample of 10,277 women and 8,190 men aged 50-96 from the SHARE survey (2004-2015), we examined self-reported BMI trajectories using multilevel linear mixed models, adjusting for confounding (birth cohorts, countries) and control (health status, health behaviours, socio-demographics) variables, and for panel attrition. Childhood information (socioeconomic circumstances and adversities) were measured with a retrospective life-course questionnaire. Results: Preliminary findings suggested that BMI trajectories were quadratic concave shaped, with BMI increasing until around 70 years of age and then decreasing afterwards. Across childhood socioeconomic circumstances strata, BMI trajectories in old age were parallel, with a consistent gradient between the less disadvantaged (lower BMI) and the disadvantaged, among men and women; except for the most disadvantaged men, whose trajectories were steep concave (higher rates of increase and decrease). Similar findings were observed for childhood adversities. Social mobility and adulthood socioeconomic circumstances were associated with BMI trajectories but did not fully mediate the childhood socioeconomic circumstances and BMI and childhood adversities and BMI associations. Discussion: These preliminary findings suggest that childhood (socioeconomic circumstances and adversities) may have long-lasting influence on trajectories of weight change in old age. The influence of childhood was not mediated by the socioeconomic life course, including social mobility.