109 patients with unilateral Colles' fracture, treated with closed reduction and cast immobilization, were re-examined after 4 (1-9) years. At follow-up, 40 patients had persistent ulnar wrist pain. The most important factor for predicting ulnar pain was final dorsal angulation of the radius. Initial and final radial shortening, fracture of the distal radioulnar joint, ulnar styloid fracture, or instability of the distal ulna were not correlated to ulnar wrist pain. We suggest that ulnar wrist pain following Colles' fracture is caused by incongruity of the distal radioulnar joint.