Osteoporosis is a public health scourge that is usually eminently preventable. Some risk factors, such as low calcium intake, vitamin D deficiency, and physical inactivity, are amenable to early interventions that will help maximize peak bone density. Other risk factors subject to modification are cigarette smoking and excessive consumption of protein, caffeine, and alcohol. Hip fractures are the most serious outcome of osteoporosis, with enormous personal and public health consequences. The ongoing Study of Osteoporotic Fractures has identified additional independent predictors of hip fracture risk, including maternal hip fracture, absence of significant weight gain since age 25, height, hyperthyroidism, use of long-acting benzodiazepines or anticonvulsants, spending <4 hours a day on one's feet, inability to rise from a chair without using one's arms, poor visual depth perception and contrast sensitivity, and tachycardia. In an individual perimenopausal woman, the risk of osteoporotic fracture and the urgency of estrogen replacement therapy can be best estimated on the basis of bone mineral density, as measured by dual-energy x-ray absorptiometry, coupled with the presence or absence of existing fractures and clinical risk factors evident from the history and physical examination. Estrogen, calcitonin, and bisphosphonates have all been proved effective in retarding postmenopausal bone loss and therefore reducing the risk of fracture. The use of sodium fluoride is more controversial, although a recent study has suggested a possible role for slow-release fluoride combined with high-dose calcium supplementation.