Osteoporosis has long been considered to be a disease of the aging female skeleton. As awareness of the pervasiveness of this disorder increases, it is clear that men are also at risk for this disorder. Recent epidemiological studies have confirmed that osteoporosis in men is an increasing health problem. This development not only has its roots in increased longevity but also in increased awareness of this problem in men. The purpose of this article is to review what is known about the factors in men that lead to acquisition, maintenance, and loss of bone, as well as new insights about the causes, pathogenesis, and treatment of osteoporosis in men.