Reproductive aging is a field that encompasses the female and male reproductive system aging and the natural ability to produce offspring in a human lifetime. The reproductive capacity of a woman varies greatly over her lifetime, diminishing over several years and finally coming to an end at menopause. Over a million U.S. women enter menopause each year. Because the average life span of humans has increased, especially in the past 100 years, more women will live a larger proportion of their lives postreproductively. Male fertility often continues through adult life, although it also diminishes with age. This page examines the aging of the reproductive system, comparing the two sexes in this regard.We discuss the patterns and consequences of endocrine changes at menopause and andropause and look at the pros and cons of therapeutically replacing the lost reproductive hormones in older adults.