The Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Disease Activity (BASDAI) are the most commonly used instruments to evaluate respectively functioning and disease activity in ankylosing spondylitis (AS).The aim of this study was to translate, adapt and validate these instruments into the Tunisian language.The studied population consisted of 68 AS patients (59 males and 9 females). Their mean age was 37.9 years (range: 18-76). The mean disease duration was 13.6 years (range: 1-40). After translation and retranslation the BASFI and BASDAI questionnaires were administrated to the patients and tested for reliability, internal consistency and construct validity.The reproducibility of the indices BASFI and BASFAI was good, the intraclass correlation coefficient for reliability was 0.96 (CCI:0.93-0.97) for the BASFI and 0.93 (CCI:0.90-0.97) for the BASDAI, and the coefficient of internal consistency (Cronbach's alpha) was 0.91 for BASFI and 0.90 for BASDAI. Concerning construct validity, both questionnaires were significantly correlated to each other, to the disease-specific instruments (BASG-s, BASMI, BASRI, ASQoL) and to all domains of the SF-36.The Tunisian versions of the BASFI and the BASDAI preserve the metrological properties of the original versions and were easy to use for the assessment of disease status in ankylosing spondylitis.