The significance of distal ulna fractures is often undermined, which can result in inadequate treatment compared with fractures of the radius, the ulna's larger counterpart. However, little guidance exists in the current literature on how to manage distal ulna head or neck fractures and intra-articular ulna head fractures. Therefore, the purpose of this retrospective study was to evaluate the outcomes of distal ulna hook plate fixation for the treatment of an unstable distal ulna fracture associated with a distal radius fracture. Twenty-five patients with unstable distal ulna fractures who underwent stable fixation for an associated distal radius fracture were included in the study. All patients achieved satisfactory reduction and bony union. Average final motion was as follows: wrist flexion, 72° (range, 60°-85°); extension, 69° (range, 65°-80°); pronation, 77° (range, 55°-95°); supination, 82° (range, 65°-90°); ulnar deviation, 35° (range, 15°-50°); and radial deviation, 24° (range, 10°-40°). Average postoperative grip strength was 28 kg (range, 22-30 kg) and was 91% (range, 71%-100%) in the cases in which the dominant hand was injured and 80% (range, 65%-100%) in the cases in which the nondominant hand was injured. Average postoperative modified Mayo wrist score and Disabilities of the Arm, Shoulder and Hand score was 87 points (range, 65-100 points) and 14 points (range, 0-54 points), respectively. Chronic instability of the distal radioulnar joint was not encountered in any patient. Thus, the study demonstrated that distal ulna hook plate fixation for the treatment of unstable distal ulna fractures can achieve healing with good alignment, satisfactory function, and minimal transient morbidity.