The clinical diagnosis of hypogonadism in the adult is difficult to establish on the basis of a history and physical examination and universally requires biochemical investigations. A serum testosterone determination is justified in men complaining of erectile dysfunction with or without alterations in sexual desire. Among the causes of erectile dysfunction, hypotestosteronemia rates are low. The prevalence of erectile dysfunction particularly is common at a period in life when alterations occur in male hormonal environment. The treatment of hypogonadal erectile dysfunction, regardless of age, is readily available, safe, and effective. The positive impact of treatment on the overall quality of life can be significant. The presence of erectile dysfunction in an aging man (> 55 years) does not imply the presence of hypogonadism, and, even if the two conditions are present, the indications for treatment require good clinical judgment. Persistent low testosterone levels may have significant detrimental effects in other organ systems; therefore, a timely diagnosis of androgen deficiency and appropriate treatment may have significant effects outside the narrow field of sexual performance.