The gradual reductions in bone mass and skeletal calcium density seen throughout adulthood occur in parallel with changes in the production of bioactive sex hormones in both men and women. The long-held belief that osteoporosis is dependent on androgens in men and estrogens in women has been challenged by recent reports of osteoporosis in young men with normal testosterone levels but extremely low estrogen levels. A review of the literature indicates that estrogens have a far greater influence on bone mass than do androgens. This may suggest new approaches to the treatment of male osteoporosis. Furthermore, osteoporosis induced by prostate cancer treatment should receive greater medical attention.