The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Bath Ankylosing Spondylitis Functional Index (BASFI) are widely used instruments in assessment of patients suffering from ankylosing spondylitis (AS). The Patient Acceptable Symptom State (PASS) is regarded as a target for patients' well-being. The aim of this study was to translate and adapt BASDAI, BASFI and PASS into the Iranian official language, Farsi, and evaluate their reliability and validity. Ninety patients with AS were included in this study. The questionnaires were translated into Farsi and back translated into English, modified until the final versions were approved with minor adaptations and the VAS was changed to numerical rating scales from 0 to 10. Forty-eight-hour test-retest agreement showed good reliability: interclass correlation coefficient (ICC) for BASDAI was 0.93 (CI at 95%, 0.90-0.95), for BASFI was 0.96 (CI at 95%, 0.94-0.97) and for PASS was 0.87 (CI at 95%, 0.79-0.92). Chronbach's alpha was 0.95, 0.96 and 0.87 for BASDAI, BASFI and PASS, respectively. BASDAI showed a significant correlation with patient global disease activity index, nocturnal back pain, total back pain, number of swollen joints, number of enthesites, morning stiffness, Bath Ankylosing Spondylitis Global Score (BAS-G), BASFI and BASMI. A significant correlation was also found between BASFI and occiput-to-wall distance, mentum-to-sternum distance, chest expansion, finger-to-floor distance, number of swollen joints, number of enthesites, nocturnal back pain, total back pain, BAS-G, BASDAI and BASMI. Patients who answered "no" to PASS (found their condition unsatisfactory) reported significantly increased pain scores, patient global disease activity scores, BAS-G, BASDAI and BASFI scores. The results showed that the Iranian versions of BASDAI, BASFI and PASS are adequately reliable and valid in patients with AS.