Testicular hormones, produced by hypothalamic-pituitary-gonadal axis activation, induce male development during embryogenesis and sexual maturation at puberty. As a consequence, any lesion at different levels of the axis is responsible for different clinical alterations, depending on the phase of life in which it develops, from early gestation to adult life. The evaluation of a hypogonadic male is complex and often diagnostic procedures only discriminate the level of damage but not the cause. Standardized and widely accepted therapies for specific forms of hypogonadism are briefly exposed. Three cases of hypogonadotropic hypogonadism are reported.