40 patients with a complete and chronic acromioclavicular (AC) dislocations were randomized to undergo surgical AC joint stabilization using either a biological graft (semitendinosus) or a synthetic ligament. The purpose was to compare these two techniques with respect to clinical and radiological outcomes. Results indicated that patients undergoing the procedure with a biological graft had significantly better Constant-Murley scores at 1 year compared to those who underwent the procedure using a synthetic ligament. This difference was not significant at the 4-year follow-up. Clinical scores did not correlate with the number of subluxated shoulders, coracoclavicular ossification, AC joint osteoarthritis, or clavicular osteolysis. Furthermore, patient satisfaction was not related to the degree of AC joint reduction.