A cohort of 74 patients with rheumatoid arthritis was monitored prospectively for 15 years. At the end of the study 148 shoulders were radiographed with a standard method. The subacromial space was examined from the radiographs with a method where the acromiohumeral interval was measured from the dense cortical bone marking the inferior aspect of the acromion to a point directly above the head of the humerus. The smallest distance was recorded, and negative values were used when the original articular surface of the humerus exceeded the inferior surface of the acromion. Destruction of the glenohumeral (GH) joints was assessed by the Larsen method on a scale of 0 to 5. The relation of subacromial space measurement to the grade of destruction of GH joints was examined. The mean subacromial space was 6.7 (SD 4.4), range from -13 to 12 mm: 6.1 mm (SD 5.6) in men and 6.9 mm (SD 4.0) in women. The mean of nonaffected (Larsen grade 0 or 1) shoulders (n = 77) was 8.6 mm (SD 1.5), and the corresponding mean of the affected (Larsen grade > or =2) shoulders (n = 71) was 4.6 mm (SD 5.5). Previously reported pathologic criterion (<6 mm) indicating rotator cuff involvement was fulfilled in 30 (20%) of 148 shoulders: in 8 (22%) of 36 shoulders in men and in 22 (20%) of 112 shoulders in women. All the shoulders with severe rheumatoid destruction (Larsen grade 4 or 5) fulfilled the pathologic limit. The subacromial space had a significant negative correlation with the GH joint destruction (Larsen grade) in both sides: right r = -.63 (95% CI -.75 to -.47), left r = -.71 (95% CI -.81 to -.58). Progressive upward migration is an inevitable consequence of rheumatoid destruction in the GH joint. A significant step in this process occurred between the Larsen grades of 3 and 4, where the mean distance turned negative, indicating rotator cuff disease. A patient with rheumatoid arthritis and painful shoulder and upward migration of the humerus on the shoulder radiograph should be evaluated by an orthopaedic surgeon. In indistinct cases with subacromial space diminution, imaging techniques like ultrasonography or magnetic resonance imaging may be required to determine the exact pathologic condition of the rotator cuff and to select optimal treatment.