A progressive decline in androgen levels is a common finding in men after middle age. The resulting clinical picture may be characterised by alterations in the physical and psychological domains, which have been demonstrated to correlate positively with testosterone serum levels. This clinical picture closely resembles the features of primary or secondary hypogonadism. Testosterone is the more convenient hormone for substitution therapy in classic hypogonadism as well as in age-related hypoandrogenism. Different choices of testosterone preparations are currently available, which are characterised by different routes of administration and by various pharmacokinetic profiles. Two major achievements urgently need to be investigated in the near future: the ability of the new formulations to reach more physiological and sustained hormone levels with the concomitant amelioration of their tolerability and the evidence of long-term prospective studies aimed at demonstrating the benefits and the possible complications of this therapy.