Anterior atlantoaxial subluxation is considered an uncommon feature of ankylosing spondylitis (AS). Six of 17 (35%) patients with spondylitis and peripheral arthritis had anterior atlantoaxial subluxation compared to none in a control group of 21 patients with AS with exclusively axial involvement (p = 0.009). Most of our patients with peripheral arthritis, with and without anterior atlantoaxial subluxation, also had an associated disorder (psoriasis, Reiter's or inflammatory bowel disease). Other features of radiologic cervical spine involvement (syndesmophytes and ankylosis) were equally present in all groups of patients (axial and peripheral arthritis, with or without subluxation). We conclude that anterior atlantoaxial subluxation is a frequent complication of the spondyloarthropathies in the presence of persistent peripheral disease and can occur in up to one third of these patients.