Primary and secondary osteoporosis are prevalent in more than 2 million American men. One of the main causes of this is hypogonadism, in turn brought upon by early androgen deprivation therapy used in prostate cancer treatment. Androgen deprivation therapy produces a host of adverse effects on the skeleton, including an increase in bone turnover, a decrease in bone mineral density, and an increase in fracture risk. In addition, based on observations in preclinical models, these adverse effects on the skeletal integrity may promote the development of or progression of metastasis to bone. Loss of bone due to androgen deprivation therapy is an important clinical issue for many men with prostate cancer, but osteoporosis is not an inevitable consequence of androgen deprivation therapy. Because of interpatient variations in peak bone mass as well as differences in rates of treatment-related bone loss, not all men with prostate cancer require treatment for osteoporosis. All men on androgen deprivation therapy should receive calcium and multivitamin supplements and should be considered for bisphosphonate therapy; this is particularly so for men with either a low baseline BMD or observed high rates of bone loss during androgen deprivation therapy.