The study aimed to map the course of the radial nerve at the posterior humeral shaft using a three-dimensional (3D) reconstruction technique based on computed tomography (CT) images of living subjects. This was to prevent iatrogenic radial nerve injury, a significant complication during surgical exposure of the humerus. The in vivo study utilized 652 upper extremity CT angiography images from 326 patients. The 3D modeling of the humerus and radial nerve was performed using AVIEW Modeler 1.0 by Coreline Soft Inc., a software capable of automatic segmentation, 3D reconstruction, and measurements. The proximal, mid, and distal points of the radial nerve on the posterior aspect of the humeral shaft were measured. The results demonstrated that the 3D reconstruction technique provides a reliable map of the radial nerve course and these measurements showed excellent intraobserver and interobserver reliability.