There are many procedures for the treatment of acromioclavicular separation but there are still controversies concerning the best management of these injuries. The cases of 20 acromioclavicular separations and 3 distal end fractures of clavicle were treated by conservative method with modified Kenny Howard sling-halter using long arm cast at the department of Orthopedic Surgery, College of medicine,Ewha Womans University, during the thirty six months period from March 1982 to February 1985. The following results were obtained. 1. The average duration of immobilization was 5 weeks at the grade II of acromioclavicular separation and fracture of distal end of clavicle and 6 weeks at the grade III of acromioclavicular separation. 2. The functional results were 17 excellents(73.8%), 5 goods(21.9%), and 1 fair(4.3%). 3. The complications were 3 frozen shoulders(13.0%), 2 subluxations(8.6%), and 1 skin necrosis on the elbow(4.3%). 4. The authors immobilized the upper extremity with long arm cylinder cast of 90° flexion position instead of initial harness, so that it was applied easily and the patient felt very comfortable. 5. When the fracture and severe displacement were occurred at the midthird of the clavicle, it could be reduced and maintained with the long arm cylinder cast and strap.