We report a prospective, randomised, controlled trial of 50 severely displaced comminuted Colles' fractures treated by either external fixation or manipulation and plaster. Each patient was assessed radiographically throughout treatment, and functionally by an independent observer at three and six months. The functional result correlated with the anatomical result, which was significantly better in patients treated by external fixation. This resulted in significantly improved function especially in young patients, and also a lower complication rate. We recommend the use of external fixation for young patients with comminuted displaced Colles' fractures unless manipulation and plaster show excellent reduction.