PURPOSE: The aim of these study is to assess the understanding of the Italian version of the IIEF-5 questionnaire (International Index of Erectile Function) and the impact of patient's demographic and clinical characteristics on it. MATERIALS AND METHODS: Each patient was asked to self complete the Italian version of the IIEF-5 questionnaire and to self report demographic information and any difficulties to complete the questionnaire and which question was considered more difficult to understand. RESULTS: A total of 89 patients were included in this study. Patients mean age was 61.2 +/- 15.4 (standard deviation = SD) years. The mean IIEF score at the time of the visit was 13.5 +/- 8.5 (SD). The questions considered more difficult to understand were number 5 (26%), number 4 (20%) and number 1 (20%). Statistically significant differences between patients with and without problems in completing the questionnaire were found in terms of education level (p = 0.0026). CONCLUSIONS: Patients with a lower educational level have more difficulties in understanding the questionnaire and the most difficult questions are items number 5, 4 and 1.