Low bone mass, in the asymptomatic patient, predicts future fracture risk as well as high cholesterol or high blood pressure predicts the risk of heart disease or stroke. In patients without fractures, osteoporosis can be diagnosed based on the extent of reduction in bone mass below mean peak bone mass of healthy young individuals. As bone mass decreases, fracture risk increases exponentially. Prevention of the first fracture is a clinical goal. Clinical situations in which an assessment of bone mass and fracture risk affects therapeutic decisions include estrogen deficiency, vertebral abnormalities, radiographic osteopenia, asymptomatic primary hyperparathyroidism, and longterm corticosteroid therapy. Serial measurements can also be used to monitor the effects of osteoporosis treatment in certain situations. The appropriate technique and skeletal site for bone mass measurements should be chosen based on the patient's circumstances. A clinical interpretation can enhance the value of computer-generated bone mass measurement reports and enhance decision making.