Osteoporosis has long been long considered a disease of the aging female skeleton. However, it is now clear that men are also at risk for this disorder. Epidemiologic studies have confirmed that osteoporotic fractures in men are an increasing public health problem, in part due to increased longevity and increased public awareness. Recent large-scale population studies in men have led to advances in our understanding of bone fragility and its treatment in men. This article reviews what is known about the factors in men that lead to acquisition, maintenance, and loss of bone, as well as new insights into causes, pathogenesis, and treatment of osteoporosis in men.