We report the long-term response to bariatric surgery in a singular family of four adolescents with severe obesity (41-82 kg/m<sup>2</sup>), homozygous for the C271R loss-of-function mutation in the melanocortin 4 receptor (MC4R), and three adults heterozygous for the same mutation. Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.