Low bone mass predicts future fracture risk as well as high cholesterol or high blood pressure can predict the risk of heart disease or stroke. Prevention of the first fracture should be a clinical goal. In patients without fractures, osteopenia and osteoporosis can be diagnosed based on the extent of reduction in bone mass below mean peak bone mass of young healthy individuals. As bone mass decreases, fracture risk increases exponentially. 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 long-term corticosteroid therapy. Serial measurements can also be used to monitor the effects of osteoporosis treatments. The appropriate technique and skeletal site for bone mass measurements should be chosen based on the patient's circumstances and the precision of measurement. A clinical interpretation can enhance the value of computer-generated bone mass measurement reports and improve decision making.