In this prospective study, ten consecutive isolated fractures of the ulna were treated by short-arm plaster cast (an average of 16.8 days) with immediate mobilization in our institution since January 1995. The minimum follow-up was eight months and the longest was two years. All fractures were closed. The median age of the patients was 36.7 years (17 to 61), the male to female ratio was 7 to 3. The patients were seen and radiographed every two weeks until bridging external callus was detected by same surgeon. Monteggia fractures-dislocation, open fractures, fractures with elbow or wrist dislocation and gunshot fractures were also excluded. The fracture involved the distal third in 5 cases, the distal quarter in 4 cases and the middle third in one case. Seven fractures were displaced between 2.5 and 6 mm, but no fracture needed reduction. All patients returned to work a mean of 4 months after the accident. Some angulation was found in most cases, but it rarely exceeded 10 degrees. In this study, the average healing time was 8 weeks and there were no non-unions. We did not encounter any synostosis between the radius and ulna in our patients. Motion at the wrist and elbow was always restored. All patients were satisfied by the functional method. The method that we have described can be safely recommended as treatment of choice for these fractures. Completely displaced, Monteggia fractures, comminuted or gunshot fractures of the ulna should be treated by other methods.