Failure to start treatment on time leads to medical and psychosocial maladjustment of the patient.AIM: Development of a method for differential diagnosis of hypogonadotropic hypogonadism and constitutional delay of puberty in boys 13.5–17 years old by scoring the levels of LH, FSH, testosterone and inhibin B.MATERIALS AND METHODS: The study group was formed by adolescent men 13.5–17 years old with delayed puberty including all observations. The gene discussed is PLOD1; the disease is hypogonadotropic hypogonadism.