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In this paper, a new method for measuring and monitoring human body joint angles, which uses wearable ultrawideband (UWB) transceivers mounted on body segments, is proposed and investigated. The model is based on providing a high ranging accuracy (intersensor distance) between a pair of transceivers placed on the adjacent segments of the joint center of rotation. The measured distance is then used to compute the joint angles based on the law of cosines. The performance of the method was compared with a flexible goniometer by simultaneously measuring joint flexion-extension angles at different angular velocities, ranging between 8 and 90°/s. The measurement errors were evaluated by the average differences between two sets of data (ranging from 0.8° for slow movement to 2.8° for fast movement), by standard deviation (ranging from 1.2° to 4.2° for various movement speeds) and by the Pearson correlation coefficient (greater than 0.99) which demonstrates the very good performance of the UWB-based approach. The experimental results have shown that the system has sufficient accuracy for clinical applications, such as rehabilitation.