BACKGROUND Distal ulna head or neck fracture is commonly associated with distal radius fracture. Treatment of these fractures remains controversial. Plate osteosynthesis is commonly performed. The purpose of this study was to observe clinical and radiological outcomes in ulna hook plate osteosynthesis for distal ulna fracture associated with distal radius fracture. METHODS This retrospective study between 2010 and 2018 included patients presenting combined displaced distal ulna fracture and distal radius fracture who were treated with ulna hook plate osteosynthesis. Patient evaluation included pain measurement with the visual analog scale, wrist range of motion, grip and pinch strengths, Quick Disabilities of the Arm, Shoulder and Hand (Q-DASH) score, and Mayo wrist score. Preoperative radiographs were reviewed to classify the distal ulna fracture according to Biyani. Bone union was evaluated on postoperative X-rays. At final follow-up, the usual radiographic parameters were measured and distal radioulnar joint (DRUJ) osteoarthritis was assessed. RESULTS A total of 48 patients were included. Mean age was 63 years old and mean follow-up was 28 months. According to the Biyani classification, there were 12 type I, 4 type II, 8 type III, and 24 type IV distal ulna fractures. Wrist flexion was 60°, extension 57°, pronation 85°, and supination 80°. Grip strength was 21 kg (86% of the uninjured opposite side). Pinch strength was 6.6 kg (92% of the uninjured opposite side). Clinical scores were very good to excellent, with a mean Q-DASH of 12 and a Mayo wrist score of 90. Discomfort or pain due to the implant that required implant removal was reported in 29%, and was higher in younger patients. Nonunion was observed in two cases and secondary implant displacement in one case. These three cases required secondary intervention with ulna head resection, which was higher in Biyani type IV. DRUJ osteoarthritis was observed in 12 patients (31%) and was higher in older patients. CONCLUSIONS Ulna hook plate fixation gives good clinical results and a high rate of fracture union, but complications are common. Implant irritation is a frequent complication, especially in young patients, and often requires implant removal. METHODS IV.