Background: Successful short-term results of diaphyseal ulna shortening osteotomy are documented in both idiopathic and post-traumatic ulnar impaction. Questions/Purposes: The purpose of this study was to evaluate the mid-term outcomes of ulnar shortening osteotomy with respect to radiographic assessment of corrected alignment and healing as well as patient satisfaction, pain, and function assessed using the Disability of the Arm, Shoulder, and Hand (DASH) score. Patients and Methods: This retrospective case series included follow-up of 33 patients with ulnar impaction syndrome following ulna shortening osteotomy at a minimum of 5 years. Patient-rated outcomes included satisfaction, pain assessment, and DASH score. Pre- and postoperative radiographs were reviewed to quantify ulnar variance and osteotomy union rates. Subsequent operations were also recorded. Results: Average follow-up was 10 years (range, 5-20 years). Eighty-eight percent of patients reported they were either satisfied or very satisfied with the procedure and 91% reported they would have the same procedure again. Average pain rating was 2 out of 10 at final follow-up. The mean DASH score was 11 (range, 0-39). Removal of hardware was performed in 10 patients (30%). The overall rate of reoperation was 45%. Conclusions: Ulna shortening osteotomy yields reliable midterm satisfaction and pain relief in patients with idiopathic and post-traumatic ulnar impaction syndrome. Reoperation is frequent. Consistent with results of short-term follow-up, plate irritation requiring removal remains the most common cause for reoperation over time.