Radial nerve paralysis associated with humeral shaft fracture is the most common peripheral nerve lesion complicating fractures. The mechanism of injury, treatment, and prognosis of radial nerve paralysis associated with fracture of the humerus vary considerably, depending on when the nerve injury occured with respect to the humeral fracture and its subsequent treatment. A clinical study was performed on 243 patients with fractures of the humeral shaft. Especially fourty two cases of radial nerve paralysis associated with fracture of the humerus were analyzed at Department of Orthopedic Surgery, Yonsei University College of Medicine from January 1965 to December 1982. The results were summarized as follows: l. Among 243 humerus shaft fractures, the ratio of male to female was 2: 1. The common cause of radial nerve paralysis associated with humerus fracture were due to traffic accident and industrial machine injury. The closed fracture was 205 cases(84.4%) and the most common type of fracture was comminuted fracture(52.6%) 2. Among 243 humerus shaft fractures, 42 cases(17.3%) complicated the radial nerve paralysis. The radial nerve paralysis was the most vulnerable to injury at the distal third of the humerus, especially when there was open or comminuted fracture. The incidence of primary radial nerve paralysis was 8%(34 cases), and 19#g(8 cases) in secondary radial nerve paralysis. 3. Among 42 radial nerve paralysis associatd with humerus fractures, 15 cases were treated by conservative method. And 27 cases were treated by surgical exploration. By surgical exploration the practical cause of radial nerve paralysis were found: 13 cases negative, 5 cases contusion, 3 cases stretching. The recovery sign of radial nerve paralysis was noted from 2 weeks after treatment. Spontaneous neurological recovery was not noted beyond 6 months after treatment. Thirty two patients were available for follow up study. The overall recovery rate of radial nerve paralysis was 81.3. The practical causes of patient with no recovery of nerve function were cross section of nerve, severe stretching or entrapment of radial nerve between the sites of fracture. From a consideration of these series, it was concluded that satisfactory result was obtained from conservative management in humerus shaft fracture associated with radial nerve paralysis. Indication of early surgical exploration of radial nerve paralysis associated with humeral fractures are open fractures requiring debridement, spiral or oblique fractures with marked displacement, and progressive nerve paralysis.