Seidel nail provides more advantages for treatment of humeral shaft fracture than other treatment modalities. It enables patients to get high bone union rate, makes surgical technigne less invasive, and allows early mobilization mobilization so that the patients is subjected to more comfortable treatment. But, Seidel nail is apt to injure the rotator cuff and has relatively weak holding power of distal fragment of fracture so that it may result in distraction and rotatory instability, and make nonunion and impaired shoulder function. Thus, in order to the functional and radiological results, complications and technical problems, we evaluated the efficacy of Seidel nail in treatment of 20 cases of hurneral shaft fractures from March l994 to March 1996, retrospectively. The results were as follows.