Abstract: Objective To study the effect of external fixation on ulna shortening deformity due to multiple cartilaginous exostosis. Methods Clinical data about six 9-13 years (mean 9.1 years) old patients (4 males and 2 females) with ulna shortening deformity due to multiple cartilaginous exostosis who underwent Orthofix external fixation in our hospital from November 2008 to February 2012 were retrospectively analyzed. Results The distal ulna increased 25-35 mm (mean 30 mm) with a good bony union. No delayed bony union occurred. The ulnar deviation malformation was corrected, the distal radioulnar joint dislocation was repositioned, the rotation function of forearm was significantly recovered, and the function of wrist and elbow joint was significantly improved.Distal needle hole infection occurred in 1 patient, which was cured after local sterilization. No fixation screw loosening was found. Conclusion External fixation can achieve good clinical outcomes in ulna shortening deformity due to multiple cartilaginous exostosis.