We evaluated ultrasound transmission velocity at the patella as an indicator of osteoporotic fragility in 293 nonobese women. Osteoporosis was defined by atraumatic vertebral compression deformity. Ultrasound velocity averaged 1954 ±71 (±SD) m/s in premenopausal normal women and declined significantly with age after menopause, largely independently of age-related loss of spine bone mass. Postmenopausal osteoporotic women had lower velocities than normal women (-76 m/s). After allowing for slight differences in age between the groups, the difference ( - 54 m/s) was still significant. Women with velocities below 1825 m/s were about six times more likely to have one or more fractures than women with velocities above that level. By sensitivity-specificity analysis, ultrasound velocity discriminated between normal and osteoporotic women as well as direct measurement of spine bone mass. Ultrasound velocity measures both bone mass and a component of bone fragility distinct from decreased mass; it is a potentially valuable new tool for evaluating women for osteoporotic fragility.