There is a consensus that interventions to prevent and treat childhood obesity should involve the family; however, the extent of the child's involvement has received little attention. The goal of the present study was to evaluate the relative efficacy of treating childhood obesity via a family-based health-centred intervention, targeting parents alone v. parents and obese children together. Thirty-two families with obese children of 6–11 years of age were randomised into groups, in which participants were provided for 6 months a comprehensive educational and behavioural programme for a healthy lifestyle. These groups differed in their main agent of change: parents-only v. the parents and the obese child. In both groups, parents were encouraged to foster authoritative parenting styles (parents are both firm and supportive; assume a leadership role in the environmental change with appropriate granting of child's autonomy). Only the intervention aimed at parents-only resulted in a significant reduction in the percentage overweight at the end of the programme (P=0·02) as well as at the 1-year follow-up meeting. The differences between groups at both times were significant (P<0·05). A greater reduction in food stimuli in the home (P<0·05) was noted in the parents-only group. In both groups, the parents' weight status did not change. Regression analysis shows that the level of attendance in sessions explained 28 % of the variability in the children's weight status change, the treatment group explained another 10 %, and the improvement in the obesogenic load explained 11 % of the variability. These results suggest that omitting the obese child from active participation in the health-centred programme may be beneficial for weight loss and for the promotion of a healthy lifestyle among obese children.