To investigate the reliability and validity of the Turkish version of the Dougados functional index (DFI) in patients with ankylosing spondylitis (AS). The Turkish version of DFI was obtained after a translation and back-translation process. Seventy consecutive patients with AS were enrolled. Patients were requested to complete the questionnaire on the day of admission (first visit), a second time within 24 h after admission (second visit), and on a third occasion. Reliability, validity and reproducibility of the Turkish version of the index were assessed. All the items showed significant correlations with the total index score with r-values ranging from 0.516 to 0.817. Cronbach alpha score was calculated as 0.908. Significant correlations were found between the total DFI score and Schober test (r = -0.293, P < 0.05), occiput-wall distance (r = 0.384; P < 0.01) finger-to-floor distance (r = 0.450, P < 0.001), chest expansion (r = -0.331, P < 0.01) and Dougados articular index (r = 0.352, P < 0.05). Good correlations were found between individual DFI items and the total score (r = between 0.533 and 0.882, p < 0.001) for the first and second visits, showing good reproducibility of the index. Conclusion: the Turkish version of DFI has good reliability, validity and reproducibility, confirming its utility for trials in Turkish AS patients.