The Cumberland Ankle Instability Tool (CAIT) is a valid instrument to determine the presence of chronic ankle instability (CAI) and to assess its severity. Self-report test is very useful for researchers and clinical practice, and CAI is a widespread tool. Nevertheless, there is lack of measurement instruments validated into Spanish, which represents a major difficulty for research dealing with a Spanish-speaking population. The questionnaire was cross-culturally adapted into Spanish. The psychometric properties tested in the Spanish version of the CAIT were measured for internal consistency, test-retest reliability, construct validity, criterion validity, and responsiveness in 108 participants who were recruited from several fitness centers. The Spanish version of the CAIT had high internal consistency (Cronbach's α = 0.766) and reliability (intraclass correlation coefficient = 0.979, 95 % confidence interval (CI) = 0.958-0.990). Correlation with the 36-item Short-Form Health Survey (SF-36) physical component summary score (rho = 0.241, p = 0.012) was greater than the SF-36 mental component summary score (rho = -0.162, p = 0.094). The construct validity shows three different factors in the questionnaire and good responsiveness with a mean change of -2.43 (95 % CI = -3.12 to 1.73, p < 0.0001) and a size effect of Cohen's d = 1.07. The Spanish version of the CAIT has been shown to be a valid and reliable instrument for measuring chronic ankle instability and constitutes a useful instrument for the measurement of CAI in the clinical setting in Spain.