The presence of anti-gliadin antibodies (AGA) and their relationship with intestinal permeability and prevalence of undiagnosed coeliac disease (CD) in ankylosing spondylitis (AS) were investigated. Blood samples from 30 AS patients and 19 age- and sex-matched controls were analysed for human leucocyte antigen (HLA)-B27, AGA and endomysial antibodies (EMA). Immunoglobulin (Ig) A-type AGA and IgG-type EMA were determined by enzyme-linked immunosorbent assay. AGA-positive patients were examined by gastroduodenoscope and proximal small bowel mucosa biopsies were performed. Eleven (36.7%) AS patients were AGA positive (compared with none of the control subjects) and three (10.0%) of these AS patients were also EMA-positive. The presence of AGA was not associated with more severe AS. Mild-to-severe villous atrophy and hyperplasia of crypts with increased chronic inflammatory cells in the lamina propria, which is typical of CD, was only observed in one AGA/EMA positive AS patient; CD was subsequently diagnosed by histology. Although AGA positivity might contribute to the pathogenesis of AS by increasing intestinal permeability to micro-organisms or by modifying intestinal immune mechanisms, further work is required to clarify its role in AS.