Numerous publications on radiation therapy of so-called “peritendinitis of the shoulder,” “subacromial bursitis,” “subdeltoid bursitis,” or “supraspinatus tendinitis” have appeared since the original report of Codman in 1904 on subdeltoid bursitis. Some of the more recent reports, notably those of McCurrach (5), Pohle (7), Steen (9), Weinberg (10), Young, B. R. (11) and Young, H. H. (12) have stressed the response to radiation. The purpose of this publication is to present the technic of treatment employed in such conditions and the results achieved in the Department of Radiology of St. Luke's Hospital (Chicago) during the past five years (January 1946–December 1950). A total of 433 patients were treated. For 318 of these the records are complete, and it is upon this group that the present paper is based. For simplification only, the term “bursitis” is used throughout. For purposes of classification and follow-up study, the cases are placed in three categories : Group I, Acute: Duration of symptoms of pain, tenderness, and limitation of motion limited to seven days or less. Group II, Chronic: Duration of symptoms over seven days. (One patient had a fourteen-year history.) Group III, Acute Exacerbation of Chronic Bursitis: This category is actually a subdivision of Group II and represents those patients who had an acute flare-up of tenderness and pain with marked limitation of motion. These patients have had previous similar attacks over periods of months or years. By classifying cases in this manner we have eliminated the “subacute” type, primarily because we feel that this is too vague and too subjective an observation and permits little uniformity in comparing or evaluating results. The primary symptom in all patients was, of course, pain of some degree, varying in intensity from minimal discomfort to excruciating pain prohibiting any motion of the shoulder joint. In all cases there was tenderness on pressure over the capsular area of the shoulder. Limitation of motion was the next most frequent complaint, especially in the chronic types, where constant pain was of less frequency. Limitation of abduction of the shoulder was quite common and attempts at abduction caused considerable pain. In approximately 55 per cent of the chronic cases the patient complained of inability to sleep comfortably; of those with acute disease, 98 per cent complained that it was impossible to sleep with the weight on the affected shoulder. Anatomy and Pathogenesis A bursa is a sac lined with synovial membrane; in the normal state it is collapsed and contains a small amount of synovial fluid. Bursae occur at points in the body where there is considerable motion between adjacent parts. Under ordinary circumstances they permit the required range of motion and, no doubt, serve their purpose more efficiently than would a more stable structure, such as a diarthrosis.