Objective-To assess the diagnostic value of ultrasonography (US) in the evaluation of arthritic shoulder joints. Methods-Twenty shoulders of 20 inpatients with arthritis were evaluated by US one day before the shoulder operation. Changes in the subacromial-subdeltoid bursa, biceps tendon and tendon sheath, rotatof cuV, and glenohumeral joint were recorded and compared with findings at operation. Results-In the detection of eVusion/ hypertrophy in the subacromial-subdeltoid bursa, US had a sensitivity of 93% and a specificity of 83%. For a biceps tendon rupture US had a sensitivity of 70% and a specificity of 100%. US missed three intraarticular biceps tendon ruptures. For eVusion/hypertrophy in the biceps tendon sheath US had a sensitivity of 100% and a specificity of 83%. For a rotator cuV tear US had a sensitivity of 83% and a specificity of 57%. US missed two small longitudinal rotator cuV tears. Three thin membranous, but intact, rotator cuV tendons were classified as full thickness tears by US. Synovial eVusion/hypertrophy was detected by US and at operation in all of the 12 glenohumeral joints that were evaluable at surgery. Conclusion-US is a reliable method in experienced hands for the evaluation of inflammatory changes of an arthritic shoulder. In advanced stages of rheumatoid shoulder joints, however, US is not useful, because destructive bone changes and tendon ruptures change the normal anatomy and restrict shoulder motions, limiting the visibility of US.