OBJECTIVE: To compare the effectiveness and safety of carbohydrate (CHO)-modified diets with a standard portion-controlled (PC) diet in obese children. STUDY DESIGN: Obese children (n=102) aged 7-12 years were randomly assigned to a 3-month intervention of a low-CHO (LC), reduced glycemic load (RGL), or standard PC diet, along with weekly dietary counseling and biweekly group exercise. Anthropometry, dietary adherence, and clinical measures were evaluated at baseline and 3, 6, and 12 months. Analyses applied intention-to-treat longitudinal mixed models. RESULTS: Eighty-five children (83%) completed the 12-month assessment. Daily caloric intake decreased from baseline to all time points for all diet groups (P<.0001), although LC diet adherence was persistently lower (P<.0002). At 3 months, body mass index z score was lower in all diet groups (LC, -0.27 ± 0.04; RGL, -0.20 ± 0.04; PC, -0.21 ± 0.04; P<.0001) and was maintained at 6 months, with similar results for waist circumference and percent body fat. At 12 months, participants in all diet groups had lower body mass index z scores than at baseline (LC, -0.21 ± 0.04; RGL, -0.28 ± 0.04; PC, -0.31 ± 0.04; P<.0001), and lower percent body fat, but no reductions in waist circumference were maintained. All diets demonstrated some improved clinical measures. CONCLUSION: Diets with modified CHO intake were as effective as a PC diet for weight management in obese children. However, the lower adherence to the LC diet suggests that this regimen is more difficult for children to follow, particularly in the long term.