The objective of our study is to analyze the impact of patient age, education level, and household income on the understanding of international index of erectile function (IIEF) and determine the patient characteristics which make this questionnaire less reliable. All men older than 18 years presenting to our clinic were asked to complete the Turkish translation of IIEF upon arrival. Self-reported information related to age, education level and household income of the patients were also recorded from the questionnaire. The patients were requested to complete the questionnaires once again, during their second visit which was not earlier than 5 hours and later than 5 days. The patients were requested to complete the questionnaire by themselves; however those who were unable to do themselves were let to receive the assistance of their companions. The answers of the questions which were replied properly were defined as "appropriate" and the unanswered questions or replied with more than one answers were defined as "inappropriate." A total of 430 patients were included in this study. Only 289 patients (67.2%) were able to respond all of the questions properly at first visit. The percentage of improper completion was increased as age increased (respectively P=0.027, P<0.001, P=0.008), whereas it decreased parallel to the increase in educational level and household income (respectively P<0.001, P<0.001, P=0.001). Of 430 patients, 68.4% did not need any help from their companions and the remaining 31.6% needed some assistance during the completion of the questionnaire. A total of 131 patients who completed the questionnaire at their initial admittance to our clinic came for their second visit. Only 61.8% of the patients were capable of completion both at first and second visit. It was found to have a low degree of consistency among the first and second administrations of IIEF (k=0.369, p<0.001). Turkish translation of the IIEF needs further validations for self-administered mode in order to improve its comprehension as well as its reliability, validity and specificity especially in older patients with lower educational level and household income status among whom the prevalence and the severity of ED is higher.