Recent advances in treatment modalitiesfor breast and prostate cancer have resulted in an increasing number of patients that are cured or that, despite residual disease, live long enough to start experiencing complications from cancer treatment. Osteoporosis is one such problem that has been increasingly identified in cancer patients. Hypogonadism and glucocorticoid use are the two major causes of bone loss in these patients. Osteoporosis is characterized by low bone mass and abnormal bone microarchitecture, which results in an increased risk of fractures. Vertebral body and hip fractures commonly result in a drastic change of quality of life as they can result in disabling chronic pain, loss of mobility, and loss of independence in performing routine daily activities, as well as in increased mortality. In patients with prostate carcinoma, androgen-deprivation therapy by either treatment with a gonadotropin-releasing hormone (GnRH) or bilateral orchiectomy results in increased bone turnover, significant bone loss, and increased risk of fractures. Patients with breast cancer are at increased risk for estrogen deficiency due to age-related menopause, ovarian failure from systemic chemotherapy, or from the use of drugs such as aromatase inhibitors and GnRH analogs. Several studies have indicated that the prevalence of fractures is higher in breast and prostate cancer patients compared to the general population. Therefore, patients at risk for bone loss should have an assessment of their bone mineral density so that prevention or therapeutic interventions are instituted at an early enough stage to prevent fractures. This article will address the characteristics of bone loss observed in breast and prostate cancer patients and potential treatments.