In a prospective study, from September 1980 to December 1984, 146 isolated ulnar shaft fractures were treated with prefabricated fracture braces. Clinical and roentgenographic follow-up data were available for 73 fractures. Functional results were rated excellent in 64 fractures (88%), good in seven (9%), and poor in two (3%). All fractures healed in an average time of 57 days. The mean angulation measured 6 degrees in the mediolateral plane and 4 degrees in the anteroposterior plane. The complication rate was 18%, relating mostly to residual angulation. Most isolated fractures of the distal one-half of the ulnar shaft can be treated successfully with prefabricated fracture braces.