Seventy-three patients had operative resection of the lateral end of the clavicle for the treatment of a painful condition of the acromioclavicular joint. Thirty-two of the patients had had a traumatic separation of the acromioclavicular joint, eight had had a fracture of the lateral end of the clavicle, and thirty-three had primary acromioclavicular osteoarthrosis. An average of sixteen millimeters (range, five to thirty-seven millimeters) was resected; the amount was similar in each of the three groups.The patients were evaluated an average of nine years (range, four to sixteen years) after the operation. The result was considered good in twenty-one patients, satisfactory in twenty-nine, and poor in twenty-three. A poor result was more common in the patients who had had a fracture of the lateral end of the clavicle (p < 0.01). Forty-six patients reported pain with exertion, and thirteen noted pain at rest. Eighteen patients had a decrease in the strength of the involved upper extremity, and sixteen had some limitation of the mobility of the shoulder. Elevation of the lateral end of the remaining part of the clavicle as compared with the scapula was noted in eighteen patients and was more likely to be associated with pain (p < 0.05). The extent of the resection was significantly associated with pain; patients who had had a smaller amount of resection (ten millimeters or less) had less pain than those who had had a larger amount (p < 0.03). A good result was more common in the patients in whom less than ten millimeters had been resected and who had had a previous traumatic separation of the acromioclavicular joint or had primary acromioclavicular osteoarthrosis.We recommend that resection of the lateral end of the clavicle be considered with caution for patients who have severe post-traumatic or degenerative osteoarthrosis of the acromioclavicular joint. If resection is performed, it should not exceed ten millimeters.