BACKGROUND Quantitative ultrasound of bone is a new radiation-free technique that measures bone mass and may assess bone quality. Retrospective studies have suggested that low-bone ultrasound of the calcaneus is associated with an increased risk for hip and other fractures in older women. OBJECTIVES To establish the utility of calcaneal quantitative ultrasound of bone for the prediction of fractures and to compare quantitative ultrasound of bone with bone mineral densitometry by performing a prospective cohort study within the Study of Osteoporotic Fractures. SUBJECTS AND METHODS We studied 6189 postmenopausal women older than 65 years of 4 US clinical centers. Broadband ultrasound attenuation (BUA), a measurement of the differential attenuation of sound waves transmitted through the calcaneus, and bone mineral density of the calcaneus and hip were measured. Subsequent hip and other nonspine fractures were documented during a mean follow-up of 2.0 years. RESULTS In age- and clinic-adjusted analyses, each SD reduction in calcaneal BUA was associated with a doubling of the risk for hip fractures (relative risk [RR], 2.0; 95% confidence interval [CI], 1.5-2.7); a similar relationship was observed with bone mineral density of the calcaneus (RR, 2.2; 95% CI, 1.9-3.0) and femoral neck (RR, 2.6; 95% CI, 1.9-3.8). After adjustment for bone mineral density of the femoral neck, BUA was still associated with an increased risk for hip fracture (RR, 1.5; 95% CI, 1.0-2.1). Intertrochanteric fractures in particular were strongly associated with a low BUA measurement (RR, 3.3; 95% CI, 2.0-5.5). CONCLUSIONS Broadband ultrasound attenuation predicts the occurrence of fractures in older women and is a useful diagnostic test for osteoporosis. The strength of the association between BUA and fracture is similar to that observed with bone mineral density.