The influence of social status on the development of body mass was analysed in a retrospective cohort study of 675 Belgian children monitored between the ages of 3 and 5 years by the preventive medical services in Brussels. At age 3, no association between excess weight and social status was observed. Adiposity rebound before age 5 was inversely related to body mass at age 3 and was independent of social status. The social influences on obesity observed in adolescence cannot be explained by a higher frequency of early adiposity rebound in children of low socioeconomic status.