Injury of the musculocutanous nerve can be associated with a proximal humeral fracture or shoulder dislocation, and injury of the brachial plexus. However, injury of this nerve associated with a humeral shaft fracture has rarely been reported. Diagnosis of the musculocutaneous nerve injury is difficult because its sensory loss is ill-defined, and examination of elbow flexion is difficult when it is associated with fractures. We report an unusual case of musculocutaneous nerve injury in a 27 years old woman who had multiple injuries including a humerus shaft fracture, an ipsilateral radius shaft fracture, and an associated radial nerve laceration. Diagnosis of the musculocutaneous nerve injury was delayed because combined fractures of the humerus and radius prevented proper examination of the elbow motion and nerve grafting of the radial nerve delayed early elbow motion exercise. Delayed exploration of the musculocutaneous nerve 6 months after trauma showed complete rupture of the nerve at its entry into the coracobrachialis muscle and the defect was successfully managed by sural nerve graft.