Testosterone deficit syndrome (TDS) is a clinical and biochemical syndrome associated with advanced age and characterized by some typical symptoms and decrease in serum testosterone levels, which can affect multiple organs and systems, deteriorating the quality of life of the males who suffer it. Due to the low specificity of the clinical picture, as well as that of the commonly used questionnaires, when there is a diagnostic suspicion, serum testosterone determination is necessary, without a current universally accepted determination method. The increased survival of males in the western world and their demand of a better quality of life,including the preservation of sexual activity, up to increasingly more advanced ages: together with the appearance of new ways of testosterone delivery, make this entity, clinical-biochemical, acquirean increasingly greater importance. From a therapeutic point of view, testosterone replacement therapy has precise indications, with individualized evaluation in each patient on the basis of risk/benefit, and with an adequate, well defined follow up, that will allow the control of possible adverse events. TRT is recommended in patients with diminished testosterone associated with muscle mass and strength loss, decrease of bone density of the lumbar spine or diminished libido and quality of erection. Contraindications for therapy would include active or non treated prostate cancer, PSA >4 ng/ml before evaluation, breast cancer, severe sleep apnea, infertility, hematocrit over 50% or severe LUTS due to BPH.