We analyzed the CT appearances of degenerative change in the atlanto-odontoid joint (AOJ) in patients with rheumatoid arthritis (RA) and evaluated the effect of these changes on atlanto-axial joint (AAJ) rotation by dynamic CT. This revealed that 9 patients (24%) treated with methotrexate had degenerative features in the AOJ. The ratio of AAJ rotation to the total rotation of the cervical spine was significantly higher in normal subjects (54+/-3%) than in patients (38+/-12%). The degree of AAJ rotation was significantly lower in the patient group with degenerative features in the AOJ (20.9+/-8.4degrees) than in patients without degenerative features (28.5+/-7.4degrees). RA patients with a history of longstanding disease and treatment with antirheumatic drugs may develop AO OA. Although secondary OA was described as healing phenomena in the joints of RA patients, it can limit rotation in the AAJ and cause suboccipital neck pain. A regular check-up of the AAJ and AOJ by means of dynamic CT in all RA patients is proposed to avoid possible antirheumatic drug complications.