The aim of this study was to determine whether socio-economical status (SES) is associated with overweight and obesity in prepuberal children. In an area of North-Western Italy a sample of 1420 children, aged 10-11 years, had his/her height and weight recorded, (overweight and obesity were defined, respectively, as relative body weight > or = 120% and > or = 140%), and parents were requested to compile a questionnaire exploring some demographic and social conditions. 23% of the sample resulted overweight or obese. Prevalence rate ratios (PRR) of overweight and obesity (together) were calculated, adjusting for parents' age, parents' area of birth, and school district. PRR for mother's lowest educational level compared to the highest was 1.59 (95% CI: 1.19-2.13), while for father's education was 1.21 (0.90-1.63). PRRs for 'unemployed' or 'manual' mother compared to 'upper non manual' were respectively 1.83 (1.20-2.79) and 2.20 (1.31-3.68), while for 'unemployed' or 'manual' father were 2.63 (1.97-2.63), and 1.63 (1.27-2.09). The cultural resources of the mother, and the economical resources of the family seem to influence the prevalence of weight gain in prepuberal children. This should be taken into account when planning programs for the prevention or reduction of obesity in children.