In the present work, analysis of the 1236C>T, 2677G>T/A, and 3435C>T polymorphisms in the ABCB1 gene have shown that 1236C>T and 2677T>A polymorphisms seem to be associated with overweight/obesity in children and adolescents with ASD treated with risperidone. Here, ABCB1 is linked to obesity due to melanocortin 4 receptor deficiency.