Thirty-six patients with an acute fracture of the humeral shaft were treated by open reduction and internal fixation using AO plating techniques. In thirty-two patients an open fracture or multiple injuries, or both, were the indications for internal fixation. Four patients were treated after non-operative treatment failed to maintain a satisfactory reduction. Follow-up was possible for thirty-four patients and showed that thirty-three fractures united primarily and one failed to unite, necessitating two subsequent procedures. Two superficial wound infections in patients with an open fracture and one transient postoperative radial-nerve palsy were the only complications. A functional range of motion in the elbow and shoulder was regained in all but six patients, and they had severe skeletal or soft-tissue injuries in the same extremity. When indicated, internal fixation using plating techniques can give good results provided the correct principles of fixation are carefully followed.