In a prospective, controlled, randomized study of acute acromioclavicular dislocations, we compared conservative and operative treatment (the Phemister procedure) with regard to the clinical results, complications, and social costs. Forty-one patients were operated on and forty-three patients were treated conservatively. Two patients who were operated on and three who were treated conservatively had to have the lateral extremity of the clavicle resected because of pain. The rehabilitation period was significantly shorter with non-operative treatment, and after thirteen months there was no difference in the clinical results. There were no serious postoperative complications, but about half of the patients who were operated on had problems with the metallic device, such as breakage or migration of the pins, or both, and six patients had a superficial infection. For most patients with total acromioclavicular dislocation we recommend conservative treatment with a sling until the patient is free of pain. Operation should be considered in thin patients who have a prominent lateral end of the clavicle, in those who do heavy work, and in patients whose daily work requires that the shoulder often be held in about 90 degrees of abduction and flexion.