Between 1984 and 1996, 8 patients who were suffered from stage g Kienbock's disease underwent interpositional arthroplasty using pronator quadratus pedicled bone. Patients comprised 2 males and 6 females, with an average age of 33 years(range 19-47). Range of motion of the wrist, residual pain, grip strength, and carpal height ratio of the patients were analyzed. The follow-up period was between 1.5 years and 12.5 years(average 5.5 years). The arc of flexion-extension of the wrist was increased from average 74 degrees preoperatively to 96 degrees postoperatively. Among eight patients, five were free of pain and three had intermittent pain during heavy work. None of eight patients had any discomfort in daily work and changed his or her occupation. The grip strength was average 83% of the normal side. Carpal height ratio was average 0.48 preoperatively and was not changed postoperatively. Clinical results, assessed by Lichtman-Evans criteria, showed 4 good and 4 fair. The interpositional arthroplasty using pronator quadratus pedicled bone was considered as a very effective method for the treatment of stage III Kienbock's disease.