A 45-year-old male patient was referred for management of radial nerve palsy. His past medical history revealed that he had been injured in a car accident and broken his left humerus 4 months ago. Primary stabilization of the fracture has been achieved by the application of a long-arm plaster cast. His medical reports displayed that he had experienced no clinical signs of radial nerve palsy at that time. After the cast was removed, he noticed that he could not extend his wrist. Surgical exploration revealed that the radial nerve was encased inside the callus. He had probably not realized the weakness of wrist extension earlier due to the structure of the long-arm plaster cast that totally encased the arm, wrist and hand. In the light of the presented case, we recommend not using a long-arm plaster cast in stabilization of the distal third humeral shaft fractures in order to diagnose this kind of a complication earlier.