Background: The International Index of Erectile Function 5 (IIEF5) is a standard questionnaire used for the evaluation of men with erectile dysfunction (ED). The Thai language version of this questionnaire is still lacking.

Objective: To develop and validate the Thai version of the IIEF5 (IIEF5-Th) questionnaire for clinical use in the Thai population.

Material and Method: The original IIEF5 questionnaire was translated into the Thai language by three experienced urologists working independently. The final version of the IIEF5-Th was obtained after consensus was reached among the three urologists and an experienced psychiatrist. The internal consistency and validity of this questionnaire was tested using Cronbach’s alpha coefficient and the weighted kappa statistic (phase 1). The test-retest reliability was checked using the intraclass correlation coefficient (ICC) for agreement (phase 2).

Results: Fifty participants with good knowledge of the English language enrolled in phase 1 and 123 participants enrolled in phase 2 of the study. The IIEF5-Th demonstrated adequate internal consistency, with a Cronbach’s alpha of 0.99. There was excellent agreement between the Thai and English versions of the IIEF5 questionnaire (weighted kappa >0.75), and the ICC for test-retest reliability was 0.92.

Conclusion: The Thai version of the IIEF5 questionnaire has a high internal consistency, and it is a valid, reliable, and useful tool for the evaluation of Thai men with ED.

Keywords: Erectile dysfunction, IIEF5, Questionnaire