Thirty elderly patients with moderately displaced Colles' fractures were randomly assigned to manipulation under Bier's block or plaster immobilization alone. Moderately displaced was defined as 10 degrees to 30 degrees of dorsal angulation and less than 5 mm of radial shortening compared with the uninjured side. The groups were well matched for age, sex, fracture type and displacement; immobilization time and rehabilitation were standardized. The outcome measures were: radiological position at union, the functional score of Gartland and Werley, grip strength, cosmesis and algodystrophy assessment. There was no detectable difference between the groups in any of the outcome measures. Two-thirds of the correction of dorsal angulation achieved by manipulation was lost by 5 weeks. We conclude that up to 30 degrees of dorsal angulation and 5 mm of radial shortening may be accepted in selected elderly patients.