BACKGROUND: Quantitative ultrasound measurement (broadband ultrasound attenuation and speed of sound) is emerging as an alternative to photon absorptiometry techniques in the assessment of osteoporosis. OBJECTIVE: To discuss briefly the fundamentals of ultrasound measurement of bone and critically review recent studies on the role of ultrasound in bone quality assessment and hip fracture prediction. CONCLUSIONS: The relationships between ultrasound and bone mineral density are too weak to allow accurate prediction of bone density at any skeletal site--including the hip--from an ultrasound measurement at the calcaneus. However, in vitro evidence indicates that ultrasound provides structural information in addition to density. In line with these in vitro data, recent prospective studies have shown that ultrasound predicts hip fractures strongly and independently of densitometry in older women.