Background: Alexithymia as a cluster of cognitive and affective deficits has been studied for its ability to predict a variety of psychological disorders. Given its clinical importance, various self-report questionnaires have been developed to measure alexithymia. The aim of this study was to determine the psychometric characteristics of Persian version of the Toronto Alexithymia Scale-20 (FTAS-20) using confirmatory factor analysis. Methods: 175 patients (102 women, 73 men) who met the DSM-IV-TR criteria for depressive, anxiety or obsessive-compulsive disorders, and 173 normal adults (99 women, 74 men) completed the FTAS-20. Results: Findings supported the three-factor structure, internal consistency, test-retest reliability, and predictive validity of FTAS-20 in both clinical and non-clinical samples. Conclusion: The three FTAS-20 subscales are useful to explore the distinct facets of the alexithymia construct.