Aim: To investigate the role of physical activity and eating behaviour in weight control 1.5 y after a weight-reduction programme in severely obese children. Methods: Forty-se-ven children (13.4± 2.1 y)were measured 1.5 y after the completion of a 10-mo residential treatment programme. Stature and body mass were measured; physical activity, fat and fibre intake, and self-efficacy in relation to physical activity and healthy eating behaviour were assessed using validated structured interviews. The total sample was divided into four subgroups according to unhealthy versus healthy physical activity and eating behaviour at follow-up. Results: One-and-a-half years after treatment, subjects had regained 34 ± 19% overweight, but were on average still 20 ± 19% less overweight than before treatment (p < 0.001). The four subgroups did not differ in level of overweight at the beginning or end of treatment. At follow-up, there was a significant difference in overweight between the four subgroups (p < 0.05). The least healthy group (unhealthy physical activity and unhealthy eating behaviour) had a significantly higher level of overweight 1.5 y after treatment (183 ± 36% ) in comparison with the other groups (unhealthy physical activity and healthy eating: 150 ± 21% ; healthy physical activity and unhealthy eating: 156 ± 14% ; healthy physical activity and healthy eating: 138 ± 16% ) (p < 0.05), whilst the healthiest group showed the lowest level of overweight after treatment when compared to the other groups (p < 0.05). Conclusion: Results suggest that both physical activity and nutritional habits play an important role in weight maintenance after initial weight loss in obese children and that one healthy behaviour can not compensate for another unhealthy behaviour. Aim: To investigate the role of physical activity and eating behavior in weight control 1.5 y after a weight-reduction program in severely obese children. Methods: Forty-se-ven children (13.4 ± 2.1 y) were measured 1.5 y after the completion of a 10-mo residential treatment program. Stature and body mass were measured; physical activity, fat and fib intake, and self-efficacy in relation to physical activity and healthy eating behaviors were assessed using valid structured interviews. The total sample was divided into four subgroups according to unhealthy versus healthy physical activity and eating behavior at follow-up. Results: One-and-a-half years after treatment, subjects had regained 34 ± 19% overweight, but were on average still 20 ± 19% less overweight than before treatment (p <0.001). The four subgroups did not differ in level of overweight at the beginning or end of treatment. At follow-up, there was a significant difference in overweight between the four subgroups The least healthy group (unhealthy physical activity and unhealthy eating behavior) had a significantly higher level of overweight 1.5 y after treatment (183 ± 36%) in comparison with the other groups (unhealthy physical activity and healthy eating Healthy physical activity and unhealthy eating: 156 ± 14%; healthy physical activity and healthy eating: 138 ± 16%) (p <0.05), while the healthiest group showed the lowest level of overweight after treatment when compared to the other groups (p <0.05). Conclusion: Results suggest that both physical activity and nutritional habits play an important role in weight maintenance after initial weight loss in obese children and that one healthy behavior can not compensate for another unhealthy behavior.