We performed ninety-six internal-fixation procedures for fracture or non-union of the humeral shaft in eighty-four patients, with a mean follow-up of 32.6 months (range, three months to fourteen years). The primary indications for operative intervention included humeral shaft fracture in a patient with multiple trauma, non-union, inadequate reduction of a humeral shaft fracture by closed methods, pathological humeral-shaft fracture, and progressive radial-nerve palsy. Methods of internal fixation included compression plates and screws and intramedullary Kuntscher nails or Rush rods. The use of an AO/ASIF compression plate or interfragmentary lag screws with an AO/ASIF neutralization plate in twenty-seven multiply-injured patients resulted in a union rate of 100 per cent and generally good motion of the shoulder and elbow. Five multiply-injured patients also obtained good results through fixation by a modified Hackethal technique using two Rush rods. The use of intramedullary Kuntscher nails resulted in a rate of union of 91 per cent in eleven multiply injured patients. Ten patients with non-union of a humeral shaft fracture had an 80 per cent rate of union with the use of an AO/ASIF compression plate. The use of a Kuntscher nail in eleven patients with non-union resulted in a rate of union of only 73 per cent and frequently caused subacromial impingement. Fractures of the humeral shaft that had had an inadequate reduction by closed means or were associated with progressive radial-nerve palsy were best managed by a compression plate or the modified Hackethal technique.(ABSTRACT TRUNCATED AT 250 WORDS)