Objectives: The purpose of the present study was to evaluate the reliability of persian version of the “Cumberland Ankle Instability Tool (CAIT)” in Iranian athletes with lateral ankle sprain.

Matterials & Methods: The present study is a methodological and non-experimental study. After forward and backward translation of CAIT, 46 athletes were selected with convenient nonprobably sampling from Physical Education Faculty of Tehran university and Taekwondo Club. Questionnaire was given to participants who experienced at least one lateral ankle sprain based on doctor’s diagnosis. In the second phase (one week later) the questionnaire was distributed among the participants again to test the reliability of the measured between the two tests. After collecting the data, the test-retest reliability of  Persian version of the questionnaire was evaluated by calculating the intraclass correlation coefficient, standard error of measurement, smallest detectable change and Cronbach’s alpha coefficients were calculated to assess the internal consistency of the questionnaire’s items.

Results Cronbach’s alpha was 0.64, which is close to acceptable level of internal consistency (0.7-0.95). Factor analysis showed that questionnaires’ items can be classified  in 4 categories with maximum of 72% variance cover. The test-retest correlation coefficient ICC for the total score of CAIT was 0.95 (P>100.0), indicating excellent reproducibility of the Persian version of the questionnaire. The standard error of measurement (SEM) was 1 and the smallest acceptable change (SDC) was 2.76 with 95% confidence.

Conclusion: The results show that the Persian version of the CAIT can be used in athletes with functional ankle instability as a reliable tool to detect instability and assess changes caused by therapeutic interventions.