The testosterone deficiency syndrome (TDS) is a very common clinical and biochemical condition that affects approximately 2-5% men over the age of 40. From a clinical point of view, it is usually associated with decreased sexual desire and activity, erectile dysfunction, low energy and mood swings, along with T<8-12 nmol/l levels. Questionnaires are not useful in screening but may be useful for diagnosis and follow-up. Its diagnosis requires the presentation of multiple hypogonadism symptoms together with two morning T tests below the acceptable limits. LH and SHBG levels can be useful to determine the cause and the free T level, respectively. Contraindications for treatment are active prostate cancer, stage IV heart failure, breast cancer, desired fertility and hematocrit values over 54%. Treatment is based on the cause of TDS, if any, along with testosterone supplementation. The objective is to achieve normal testosterone levels. Follow-up includes clinical history, analysis (PSA, T+SHBG, hematocrit, glucose and lipid profile) and rectal examination, 3, 6 and 12 months after beginning treatment.