Signs and symptoms conforming to the "painful shoulder syndrome" may be caused by arthritis of the acromioclavicular joint. In the author's cases, the clinical manifestations were indistinguishable from those produced by arthritis of the shoulder joint, subacromial and subdeltoid bursitis, and radicular neuralgia. Both the clinical and the roentgenographic findings suggested osteo-arthritis or traumatic arthritis. Roentgenotherapy in very small doses resulted in clinical cure in a series of patients. Other modes of treatment had not been effective.