Background Biomechanical studies comparing various surgical techniques for acromioclavicular joint reconstruction have reported that semitendinosus tendon graft for coracoclavicular ligament reconstruction provides a substantial improvement in initial stability and a load-to-failure equivalent to the intact coracoclavicular ligaments. Although it represents a biomechanical improvement compared with coracoacromial ligament transfer, there is still a lack of prospective comparative studies confirming the clinical relevance of these biomechanical findings. Hypothesis Semitendinosus tendon graft for coracoclavicular ligament reconstruction is associated with superior clinical results compared with a modified Weaver-Dunn procedure in chronic complete acromioclavicular joint dislocation. Study Design Cohort study; Level of evidence, 2. Methods Twenty-four patients (mean age, 42 years) with painful, chronic Rockwood type III through V acromioclavicular joint dislocations were subjected to surgical reconstruction. In 12 patients, a modified Weaver-Dunn procedure was performed; in the other 12 patients, autogenous semitendinosus tendon graft was used. Clinical evaluation was performed using the American Shoulder and Elbow Surgeons shoulder score and the Constant score after a mean follow-up time of 37 months. Preoperative and postoperative radiographs were compared. Results The mean American Shoulder and Elbow Surgeons shoulder score improved from 74 ± 7 points preoperatively to 86 ± 8 points postoperatively in the Weaver-Dunn group, and from 74 ± 4 points to 96 ± 5 points in the semitendinosus tendon group (P < .001 for both techniques). The mean Constant score improved from 70 ± 8 points to 81 ± 8 points in the Weaver-Dunn group, and from 71 ± 5 points to 93 ± 7 points in the semitendinosus tendon group (P < .001). The results in the semitendinosus tendon group were significantly better than in the Weaver-Dunn group (P < .001). The radiologic measurements showed a mean coracoclavicular distance of 12.3 ± 4 mm in the Weaver-Dunn group increasing to 14.9 ± 6 mm under stress loading, compared with 11.4 ± 3 mm increasing to 11.8 ± 3 mm under stress in the semitendinosus tendon group. The difference during stress loading was statistically significant (P = .027). In the semitendinosus tendon group, horizontal displacement of the lateral clavicle end could be reduced in all cases with type IV dislocation. Conclusion Semitendinosus tendon graft for coracoclavicular ligament reconstruction resulted in significantly superior clinical and radiologic outcomes compared to the modified Weaver-Dunn procedure.