Hypogonadotropic hypogonadism in the male is caused by alterations in gonadotropin-releasing hormone secretion or through abnormal pituitary secretion of luteinizing hormone or follicle-stimulating hormone. Recent studies in animal and human models have demonstrated possible pathophysiologic explanations for the occurrence of some GnRH-deficient states. It is critical to ascertain whether such patients represent a variant of normal or have true hypogonadotropic hypogonadism. Recent developments in both diagnostic techniques and hormonal treatment increase the chances of a correct diagnosis and successful treatment outcome.