In a prospective study 52 patients with an isolated fracture of the distal ulna were treated with a below-elbow plaster cast. The histories of 46 patients were reviewed after a mean follow-up of 3.5 years (ranging from 10 months to 7 years). Forty-three fractures united. There were two non-unions. One fracture displaced while in the plaster, so that there was no longer any bone contact between the fragments. The fracture was consequently treated by open reduction and internal fixation. The type of fracture, the initial displacement (all fractures had bone contact) or the initial angulation (maximum 10 deg) was not found to influence the final clinical results. Below-elbow plaster cast appeared to produce satisfactory results in 89% of the patients.