OBJECT: To analyze the influence of socioeconomic status on the prevalence, evolution and incidence of obesity between the ages of 12 y and 15 y in Belgium. DESIGN: Retrospective cohort study. SUBJECTS: 2607 children from five social groups. MEASUREMENTS: The body mass index (BMI) measured during two school medical examinations carried out at an interval of two years between the ages of 12 y and 15 y. RESULTS: Between the ages of 12 y and 15 y the inverse relation between social status and the prevalence of obesity is accentuated in girls. The increasing divergence between social groups was a result both of the greater incidence of new cases of obesity and the reduced improvement rate in obesity already present in adolescents of lower social classes. CONCLUSIONS: Social inequalities in obesity increase during early adolescence. Preventive measures, targeting children of low socioeconomic status, should be put in place at this stage of life. | 
