Seven cases of posterior interosseous-nerve palsy, three associated with ulnar-nerve palsy as a complication of Monteggia lesions have been presented. The posterior interosseous nerve may be stretched by the dislocated radial head, or compressed within the Arcade of Frohse. Ulnar-nerve injuries are secondary to compression within the cubital tunnel. Surgical decompression of the nerves appears to be the treatment of choice.