PURPOSE: To evaluate the treatment outcomes of the modified extension block technique for bony mallet finger. MATERIALS AND METHODS: This study included 16 patients who had been treated with the modified extension block technique for bony mallet finger from December 2002 to January 2004. The average duration of follow up was 13 (12~17) months. The indication of operation was the presence of a large bony fragment invading more than 1/3 of the articular surface or the palmar subluxation in the distal interphalangeal joint. RESULTS: The average extension lag was 2.3 degrees, and the range of motion of the distal interphalangeal joint was 68.8 degrees. Radiograph showed bony union state in all cases. By the Crawford's evaluation criteria, 12 cases (75%) was excellent or good. Postoperative complications occurred in 3 cases, which were reduction loss within postoperative 2 weeks in 2 cases and mild pain with motion in 1 case. CONCLUSION: The modified extension block technique is a easy and simple method. It shows a good result without complications from skin incision. So, it seems a useful method for bony mallet finger.