The aims of this study were to assess the frequency of obesity, hypertension, metabolic syndrome, insulin resistance, and dyslipidemia in a sample of child and adolescent users of risperidone, to evaluate associations with clinical and pharmacological data and with certain polymorphisms of the HTR2C, DRD2, LEP, LEPR, MC4R, and CYP2D6 genes. The gene discussed is MC4R; the disease is obesity due to melanocortin 4 receptor deficiency.