The initial testicular size usually reflects the severity of gonadotropin deficiency and predicts the increase in testicular volume in response to treatment in patients with delayed puberty and hypogonadism, so we use it as a guide for selecting the initial treatment option. We use both hCG and FSH in an adolescent boy with a previous history of absent puberty and small testicular size. This evidence concerns the gene BRD2 and Gonadotropin deficiency.