The objective of this paper is to assess the effect of the socio-economic status (SES) on long-term outcomes of a family-based obesity treatment intervention in prepubertal children. A total of 52 overweight and 26 normal weight children were investigated. Nutritional status, intake of fruit, vegetables and low fat foods, in-between meals, sports club membership, frequency of exercise and daily television viewing were measured before intervention (t[subscript 0]) and after a mean period of 1.3 years (t[subscript 1]). The result obtained indicate that a low SES may serve as a barrier against family-based intervention. The data provide evidence for the idea that there is need for social stratification of future measures of health promotion within families. (Contains 4 tables.)