We treated 27 cases of the complete dislocation of the acromioclavicular joint with the modified Weaver and Dunn procedure described by Shoji et al, which is resection of the lateral end of the clavicle and bone block transfer of the coracoacromial ligament, from July 1987 to December 1989. Twenty-one patients were followed for an average of fourteen months and the brief summary of the observations are as follows: 1. The peak incidence was in 3rd and 4th decades and much more prevalent in male (76%). 2. The most common cause of the injury was traffic accident and followed by fall down. 3. In functional evaluation by the Weitzmann criteria, an excellent result was seen in fourteen cases; a good result, in five; a fair result, in two. 4. The comparision of the coracoclavicular interval ratio before surgery with that after surgery facilitated the evaluation of the effectiveness of the coracoclavicular ligament reconstruction. 5. There were no major complications that could affect to end result.