The aim of this study was to assess distal radioulnar joint stability after unipolar ulnar head replacement for post-Darrach instability. All the patients who underwent ulnar head replacement between1999 and 2015 for post-Darrach procedure instability at our clinic were reviewed. Seven Hebert-type and two uHead (SBI/Stryker) prostheses were implanted. None of the implants were cemented. We assessed stability, pain, range of motion and strength pre- and postoperatively. The changes in the radiographic appearance between immediate postoperative and the last follow-up were determined. All patients (8 patients and 9 joint replacements) had a stable distal ulnar stump at the mean follow-up of 69 months. No complications occurred and no revisions were needed. Pain on a visual analog scale (VAS) was 0 at rest and 6 during maximum effort at the last follow-up; it was 1.5 at rest and 8.5 during effort preoperatively. Wrist flexion and extension, supination and grip strength were unchanged. Pronation increased from 45° to 70°. An area of bone resorption proximal to the ulnar head implant was found in 5 cases but no secondary displacement of the implant or increased pain was reported. Ulnar head replacement stabilizes the ulnar stump. The implant acts as a spacer to place the soft tissues under tension. Distal ulnar stump instability after the Darrach procedure can be solved by a unipolar ulnar head replacement procedure.