The aging of humans is a recent evolutionary event. Of the thousand generations of men and women who have lived on this planet, only the humans of the last two generations could have hoped to live past the age of 50. The population is getting proportionally older. The number of people 85 years of age and older today is substantially greater than at the beginning of the 20th century. Advancing age is associated with decreased muscle mass and strength, and impairment of physical, sexual, and cognitive functions. Diminished muscle mass and strength increases the risk of falls, disability and poor quality of life. Age-related impairment of sexual and cognitive functions also contributes to overall reduction in quality of life. Testosterone replacement, by improving some aspects of physical, sexual and cognitive functions, would be expected to improve health-related quality of life.