Objective: The purpose of this study was to determine the knowledge levels of university students about sexually transmitted diseases (STD) and differences in knowledge levels in relation to sociodemographic variables. Materials and methods: This descriptive study was carried out among 330 students (207 females, 123 males) of Buca Education Faculty of Dokuz Eylul University, Izmir. Data were collected using an information form designed by the authors and a 36-item Knowledge Test for Sexually Transmitted Diseases adapted from the 40-item STI/HIV Pre-test. Results: The frequency of having at least one sexual intercourse was 27% (n= 89). Of these, 45% (n= 40) reported sexual intercourse with the same partner within the past year, and 69.7% (n= 62) reported contraceptive use during sexual intercourse. The majority of the students did not receive sexual health education during high school (65.8%) and university (84.9%). The number of correct responses in the Knowledge Test for STDs ranged from 3 to 34. The mean scores for correct, incorrect, and "don't know" answers were 25.00 +/- 5.09, 3.04 +/- 2.24, and 10.15 +/- 6.11, respectively. It was found that male sex (t= 2.47, p< 0.05), having a history of sexual intercourse (t= 3.83, p< 0.001), the use of a contraceptive method (t= 3.21, p< 0.01), and having sexual health education during high school (t= 2.10, p< 0.05) were significantly associated with higher knowledge levels about STDs. Conclusion: Our data showed that university students had a moderate level of knowledge about STDs, and that their levels of lack of knowledge were greater than levels of incorrect knowledge. We suggest that the knowledge levels of university students about STDs be increased and sexual health education programs be implemented in order to reduce or prevent the incidence of STDs.