Purpose: The aim of this study was to adapt the Cleveland Adolescent Sleepiness Questionnaire into Turkish, and evaluate its suitability for high school students. Materials and Methods: The cross-sectional study was carried out with 329 students in a high school. Data were collected using the data collection form, Epworth Sleepiness Scale and Cleveland Adolescent Sleepiness Questionnaire between January and February 2019. Results: Confirmatory factor analysis confirmed the four-dimensional original structure of the scale. The fit indices of the scale; Chi-square test (chi 2=172,78, df=96, p=0,001), Root Mean Square Error of Approximation=0,049, Comparative Fit Index=0,98, Normed Fit Index=0,96, Non-Normed Fit Index=0,98, Goodness Of Fit Index=0,94, Adjusted Goodness of Fit Index=0,91 showed a perfect fit. Factor loads of items ranged between 0,58 and 1,13, and t values were found to be significant. The reliability coefficient of the scale was found to be 0,87 with high reliability. In addition, a moderate positive and significant relationship (0,638) was determined between the Epthworth Sleepiness Scale and the Cleveland Adolescent Sleepiness Questionnaire, a measure of sleepiness, and a criterion-related validity was established. Conclusion: Cleveland Adolescent Sleepiness Questionnaire is a valid and reliable measurement tool in determining the sleepiness of high school students.