Objective: The aim of this study was to develop a Turkish version of the Bath Ankylosing Spondylitis Functional Index (BASFI) and Dougados Functional Index (DFI) and assess their reliability, validity, and sensitivity to change. Methods: The Turkish versions of the BASFI and DFI were obtained after a translation and back-translation process. Seventy-one patients with ankylosing spondylitis (AS) were included in the study. For investigation of the reliability of the BASFI and DFI, 36 of the patients recompleted both indices on the following day. To assess validity, the patients were evaluated with the Bath AS Disease Activity Index (BASDAI), Bath AS Metrology Index (BASMI), Bath AS Patient Global Score (BAS-G), physicians' assessment of disease activity, Bath AS Radiology Index-spine (BASRI-s) and sacroiliac joints, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). To assess the sensitivity to change, 16 patients were included in an 8-week home exercise program. In addition, 16 who had been on nonsteroidal anti-inflammatory drug (NSAID) treatment were requested to stop the treatment for 1 to 2 weeks. Resutls: There were no significant differences in BASFI and DFI scores on two occasions within 24 h (P > 0.05). The results showed correlations between both of the functional indices and the aforementioned validation parameters except ESR, CRP, and radiologic changes in the sacroiliac joints. The BASFI and DFI scores and BASMI and BASDAI values showed significant improvements in the home-exercise group. For the group of patients whose NSAIDs were stopped, BASFI, DFI, and BASDAI scores showed significant increase, whereas the mean BASMI score did not change. Conclusion: The results indicate that the Turkish versions of the BASFI and DFI are reliable, valid, and sensitive to change.