Osteoporosis, characterized by low bone mineral density, is common and associated with an increased risk of fracture. The lifetime risk of an osteoporotic fracture is approximately 50% for women and 30% for men. Osteoporotic fractures can cause significant pain and disability. As such, research has focused on means of preventing osteoporosis and related fractures. Primary prevention strategies include calcium supplementation, vitamin D supplementation, and exercise programs. A recent systematic review and meta-analysis found that calcium supplementation of 1200 mg per day or more (with or without vitamin D) could decrease fracture risk for adults (mainly women were studied) over age 50. Screening for osteoporosis on the basis of low bone mineral density is also recommended for women over age 60, based on indirect evidence that screening can identify women with low bone mineral density and that treatment of women with low bone density with bisphosphonates is effective in reducing fractures. The effectiveness of screening for osteoporosis in younger women and in men has not been established. In addition, real-world adherence to pharmacologic therapy for osteoporosis is low: one-third to one-half of patients do not take their medication as directed. Vitamin D deficiency is common and can increase the risk of fracture. Screening to detect vitamin D deficiency in older adults has been proposed, but has not yet been rigorously evaluated.