The overall objective of this research is to develop an ultrasonic system for noninvasive assessment of the distal radius. The specific objective of this study was to examine the relationship between geometrical features of cortical bone and ultrasound measurements in vitro. Nineteen radii were measured in through transmission in a water bath. A 3.5 MHz rectangular (1 cm x 4.8 cm) single element transducer served as the source and a 3.5 MHz rectangular (1 cm x 4.8 cm) linear array transducer served as the receiver. The linear array consisted of 64 elements with a pitch of 0.75 mm. Ultrasound measurements were carried out at a location that was 1/3rdrd of the length from the distal end of each radius and two net time delay parameters, tau(NetDW) and tau(NetCW), associated with a direct wave (DW) and a circumferential wave (CW), respectively, were evaluated. The cortical thickness (CT), medullar thickness (MT) and cross-sectional area (CSA) of each radius was also evaluated based on a digital image of the cross-section at the 1/3rd location. The linear correlations between CT and tau(NetDW) was r = 0.91 (p < 0.001) and between MT and tau(NetCW) - tau(NetDW) was r = 0.63 (p < 0.05). The linear correlation between CSA and a nonlinear combination of the two net time delays, tau(NetDW) and tau(NetCW), was r = 0.95 (p < 0.001). The study shows that ultrasound measurements can be used to noninvasively assess cortical bone geometrical features in vitro as represented by cortical thickness, medullar thickness and cross-sectional area.