Ultrasound transmission velocity and ultrasound attenuation of the appendicular skeleton are influenced by bone density and by bone structure and correlated to mechanical properties of bone. This article reviews basic principles of these techniques and their experimental and clinical applications. Results of the ultrasound techniques and their relation to established radiological measurements for the assessment of bone mineral density in vivo and in vitro are reported. Factors with an influence on both ultrasound transmission velocity and ultrasound attenuation are discussed. Ultrasonic measurements of the bone may offer a simple, non-invasive and radiation-free assessment of bone quality in osteoporosis and other metabolic diseases affecting the bone. However, further studies are required to confirm this.