We found that 14 of 162 rheumatoid arthritis patients with chronic occipitocervical pain had anterior atlantoaxial instability in the absence of any corresponding radiographic changes in the joint cartilage or subchondral bone. Our findings suggest that ligamentous instability is a prerequisite for this type of change. At the time of the detection of the instability, the median duration of disease was 12 (6-28) years. Rheumatoid occipitocervical pain may be initially caused by facet-joint arthritis or inflammation in the ligaments, and at a later stage also by irritation of the C2 nerve roots.