Involvement of the upper cervical spine, with possible instability and dislocation of the atlanto-axial-cervico-occipital joints in patients with rheumatoid arthritis (RA), is routinely monitored with conventional radiographs. As disease progresses severe interpretation problems occur, especially when looking for cranial migration of the odontoid process. The aim of the present study was to evaluate whether three dimensional CT examination should be considered for such monitoring. After clinical and biochemical examination of 20 consecutive patients, diagnostic information about cranial migration of the odontoid process was obtained by conventional radiograms and by three dimensional CT examination. When using conventional radiographs the odontoid process and the its relation to the skull base could be outlined in 8 of the 20 patients. whereas all bony structures could be well demonstrated on the CT examination and the degree of cranial migration into the foramen magnum could be quantified. Three dimensional CT should be considered as a reliable examination for monitoring RA patients with involvement of the upper cervical spine and a possible cranial migration of the odontoid process.