Seidel nail is one of locked humeral nail and Seidel himself reported excellent result in his preliminary report using his nail. But our early experience showed disappointing result with high rate of complications, So we reviewed our 16 cases of humeral shaft fracture with polytrauma treated with Seidel nail and studied anatomical fitness of the nail within the distal medullary space using CT scan. The most frequent complication was intraoperative fracture of the proximal humerus<4 cases> and this seemed to be due to lateral placement of pilot hole. There were 3 cases of nonunion and these cases showed insufficient distal anchorage, either primarily or postoperatively. Anatomical fitness study showed insufficient spreading of nail flanges in 5 cases of distal canal width below 9mm and nonunion cases were in this group. Other problems of Seidel nail were technical difficulties due to occasionally incorrect proximal targeting device and frequent breakage of adaptor screw. Study of more cases may be needed to confirm the design problem of Seidel nail.