Testosterone therapy has been reported to be useful in the treatment of hypogonadism and partial androgen deficiency of the aging male (PADAM) syndrome. Testosterone administration is needed in order to maintain secondary sexual characteristics, muscle mass, bone mineral density, cognitive function and sexual drive. Newer testosterone-containing compounds, particularly gel preparations, are known to produce more stable circulating testosterone levels than im-administered drugs, with scarce side-effects and good patient compliance. All patients treated with testosterone must undergo a careful follow-up to prevent the development of the major side effects, such as sleep-apnea, erythrocytosis, cardiovascular diseases and the alterations of hepatic function and plasma lipid concentrations.