The behaviour of the bony deformity in Colles' fractures and factors influencing this were prospectively investigated in 187 patients over the age of 55. Radiographic assessment was made throughout a 13-week period and during this time the deformity progressively recurred, even after the plaster cast had been removed. Radial length and radial deviation reverted virtually to their positions before reduction. Only those fractures with a volar tilt greater than -15 degrees when first seen showed any improvement. In all fractures the initial deformity clearly influenced the final radiological result whereas the quality of reduction was not of critical importance. The extent of dorsal comminution and quality of the bone influenced the final anatomical result in those fractures which were not manipulated.