A 43-year-old female patient underwent pyelolithotomy in the left lateral decubitus position. Her upper right arm was placed on a padded armboard. Surgery lasted for 240 min. Postoperatively, she complained of numbness of the dorsal part of her right hand and wrist drop. Neurological examination revealed hypoaesthesia of the dermatome of the right forearm and hand innervated by the radial nerve. Electromyography revealed advanced axonal degeneration of the radial nerve below the level of the elbow. Treatment with diclofenac, vitamin B and physiotherapy was started. Her symptoms improved gradually and at the 60th postoperative day, motor weakness had completely resolved. In order to prevent peri-operative nerve injury, careful positioning of every patient on the operating table with proper padding is essential, with attention paid to time-dependent risks. If an injury occurs, diagnosis and treatment should be started as rapidly as possible.