Background Kienböck disease is an aseptic necrosis of the lunate of unknown etiology, prevalent in young adults. Treatment aims to lower forces on the lunate, decrease pain and improve function. We conducted a retrospective evaluation of the 10-year clinical and radiological outcomes of radial osteotomy as a treatment for Kienböck disease. Materials and Methods We analyzed pain, grip strength, wrist range of motion (ROM), radiological carpal geometry, and staging of osteoarthritic changes over a 10-year period, postosteotomy, for 18 patients. The Mayo wrist score was used as an overall measure of outcome. Technique Outcomes for two types of osteotomies were included, a step-cut osteotomy with fixed screws and an updated technique of two linear transverse osteotomies with volar locking plates. For cases with negative ulnar variance, resection of the radius was included to obtain a final ulnar variance of -1 to 0 mm. For positive ulnar variance, the goal was to obtain a correction of radial inclination of 10 to 15 degrees. Results Improvements in pain, ROM, and grip strength were maintained over the 10-year follow-up, without radiological improvement in geometry (carpal height ratio and Stahl index). Mild osteoarthritic changes were identified in 33% of patients, with no effect on clinical results. Degree of cartilage damage determined postoperative grip strength improvement. The Mayo wrist score at the final follow-up was excellent in one patient, good in nine, and fair in eight. Conclusions Radial osteotomy provides reasonable and long-term clinical benefits. Preoperative arthroscopic evaluation of cartilage damage can inform treatment decisions.