The effect of involvement of the distal radio-ulnar joint on subsequent function was studied in 170 patients with Colles' fractures, reviewed for one year after cast removal. Patients with involvement of this joint had significantly weaker grips and a significantly greater incidence of pain and tenderness over the joint at all stages of follow-up. They also had a poorer range of supination at six months and at one year. The presence or absence of an ulnar styloid fracture was not related to the functional results.