Osteoporosis and osteoporotic fractures are generally considered to mainly affect older postmenopausal women, but up to 20% of symptomatic vertebral fractures and 30% of hip fractures occur in men. Osteoporotic fractures in men are associated with substantial morbidity, greater excess mortality than in women and account for almost 25% of the cost of osteoporotic fractures in the UK. One of the major secondary causes of osteoporosis in men is hypogonadism, which is found in up to 20% of men with symptomatic vertebral fractures and 50% of elderly men with hip fractures. This chapter outlines the pathogenesis of osteoporosis in men, placing particular emphasis on the importance of sex steroids in the maintenance of bone health. The effects of hypogonadism on the skeleton are described, as well as the consequences of androgen deprivation therapy in men with prostate cancer. Finally, we review the effects of testosterone replacement in hypogonadism and explore other options for the treatment of osteoporosis secondary to loss of sex steroids in men.