In a prospective study of Colles' fractures, 100 patients with Older type 1 and 2 fractures were randomized in two groups. One group was immobilized for 3 weeks and the other one for 5 weeks. Both groups were immobilized with a below-elbow plaster splint. At 1 year follow-up, there were 73 patients with 74 fractures. Dorsal angulation, radial length, wrist motion, grip strength and pain were measured. There was no significant difference in the measured parameters in the two groups. We found that 3 weeks of immobilization is a satisfactory treatment for Older type 1 and 2 Colles' fractures.