Male hypogonadism is a heterogeneous condition whose diagnosis is challenging. The coexistence of low testosterone (T) and consistent clinical features is necessary. T requires multiple and consistent laboratory results from reliable centers. Clinical features of hypogonadism are a wide array. The most specific of these are those characterizing the rarest forms. In the most frequent forms, clinical features are subtle and the most specific symptoms are sexual ones. However, clinicians should be aware that most of hypogonadism’s clinical features greatly overlap with those of ageing and chronic illnesses; in addition, hypogonadism may be an epiphenomenon rather than a cause. This makes it particularly challenging to identify correctly the so-called late-onset hypogonadism, a condition occurring in adult men because of ageing, metabolic disorders, and systemic chronic morbidities. A correct diagnosis is pivotal because treating hypogonadism provides the best results in men whose symptoms are actually dependent on T deficiency. T therapy provides beneficial effects on sexual function and body composition. The effects on glycolipid parameters are mild and inconsistent whereas the effect on bone and mood, despite apparently positive, requires more evidence. Gonadotropin (and GnRH) therapy is the approved option for secondary hypogonadal men seeking fertility in the short term.