The purpose of this study was to evaluate the clinical and radiological results of a modified Phemister method reinforcing the 4 strands of an Ethibond sling for acromioclavicular joint dislocation. Materials and Methods: Between September 1999 and May 2007, 30 acromioclavicular joint dislocation cases underwent a modified Phemister method reinforcing the 4 strands of an Ethibond sling. The average follow-up period was 28.2 months (range: 24~33 months). Clinical outcomes were evaluated using the Weitzman classification; the state of coracoclavicular space reduction was done using radiologic findings. Results: According to the Weitzman classification, there were 24 excellent, 4 good and 2 fair case outcomes. The average coracoclavicular distance improved from 16.9 mm to 7.3 mm immediately after surgery. The average ratio of coracoclavicular distance comparing to the contralateral side at the final follow-up was 1.24 (range: 0.68~1.71). Complications included retraction of K-wires in 5 cases and restriction of joint motion in 4 cases. Conclusion: The modified Phemister operation using augmentation of the coracoclavicular ligament by 4 strands of Ethibond is an effective treatment modality in acromioclavicular joint dislocation.