In a retrospective analysis of 450 patients with rheumatoid arthritis the cervical films were reviewed to detect vertical dislocation of the C1 and C2 vertebrae. A frequency of 10 per cent was found among all patients and of 24 per cent among those with cervical arthritis. The authors' method of measuring vertical dislocation at conventional radiography turned out to be superior to the method of McGregor , especially in cases with severe dislocation. The vertical dislocation was shown to be preceded by a horizontal dislocation and the appearance of vertical dislocation diminished or abolished the horizontal dislocation. Progression occurred in many cases and was combined with erosions of the atlas and axis. In more than half of the patients there was also contemporaneously a subaxial dislocation. Neurologic symptoms were more often occurring in patients with a severe vertical dislocation and in patients with spinal stenosis at the C1 level.