Obesity in children is associated with vitamin D (VD) deficiency and cardiometabolic abnormalities. To analyze the effects of VD supplementation in adolescents with obesity enrolled in a weight-loss program. Adolescents with obesity (n=26) and with normal weight (n=23; controls) were matched for age, sex, and puberty stage. The obesity group followed a 3-month weight-loss program that combined a reduced caloric intake with interval training physical activity and during which they received or not VD supplementation (4000 IU/d) (n=13/group; random assignation). The anthropometric parameters (BMI z-score, fat mass); serum levels of 25(OH)D, calcium and parathyroid hormone (PTH), cardiometabolic factors (triglycerides, HDL, and LDL cholesterol), fasting glucose and insulin, and homeostasis model assessment of insulin resistance index; diastolic, systolic and mean blood pressure, and inflammatory status (C-reactive protein, CRP) were measured at baseline and at the end of the 3-month program. At baseline, 25(OH)D concentration was lower and VD insufficiency (25(OH)D levels <50 nmol/L) rate was higher (73% vs 22%) in the obesity than in the normal-weight group. All cardiometabolic factors were altered in the obesity compared with the normal-weight group. After the 3-month weight-loss program, 25(OH)D levels was >50 nmol in all adolescents with obesity, but only in 46% of normal-weight adolescents. Moreover, the weight-loss program improved the cardiometabolic factors, inflammatory status (CRP) and physical performance, but VD supplementation did not have any additional effect. Analysis only of the adolescents with obesity and VD deficiency (25(OH)D <50 nmol/L) at baseline showed a significant correlation between the change in PTH and CRP (p=0.02) in the supplemented obesity group, while the increase in 25(OH)D only tended to be correlated with CRP decrease. Vitamin D supplementation could reduce VD insufficiency in adolescent with obesity, but does not have any additional effect on cardiometabolic factors when combined with a weight-loss program.