The decrease in testosterone levels with age is both central (pituitary) and peripheral (testicular) origin. Because serum levels of sex-hormone-binding globulin increase with aging, the decrease in free testosterone is of even greater magnitude. Recent long-term studies of testosterone therapy in hypogonadal elderly men have shown beneficial effects on bone density, body composition, and muscle strength without any substantial adverse effects on lipids and the prostate. Total testosterone level is the test of choice for initial screening of elderly men who present with signs and symptoms of hypogonadism. If the level is below 300 ng/dL, replacement therapy should be initiated. If the level is normal in a symptomatic patient, free or bioavailable testosterone should be determined. The pros and cons of testosterone therapy should be discussed in depth with every patient, and decisions should be made on an individual basis. This review summarizes the trials of testosterone replacement therapy in elderly men and outlines a diagnostic approach to these patients.