BACKGROUND Human immunodeficiency virus (HIV) transmission pattern in Iran has been changed from injection drug to sexual contact. Lack of accurate assessment of HIV in people with sexually transmitted diseases (STDs) in Iran prompted us to conduct this study to determine the frequency of HIV infection in these patients. METHODS In this cross-sectional study which conducted in 2016-2017, overall, 190 patients with STDs referring to two hospitals of Hamadan were enrolled in the study. All of the patients were examined for HIV in the first visit by rapid test and then 1 and 4 months later by the 4th generation ELISA. A questionnaire including demographic data, clinical manifestations, and high-risk behaviors was completed for all of the referring people. The collected data were analyzed using appropriate statistical tests. RESULTS Of 190 patients, 126 (66.3%) were female with a mean age of 34.1 ± 10.1 years and 64 (33.7%) were male with a mean age of 30.8 ± 7.8 years. One hundred twenty-eight (67.4%) got married, 73 (38.4%) and 76 (40%) had a diploma and postgraduate education, respectively, 32 (16.8%) mentioned the history of unsafe sex, and 23 (12.1%) had used condoms continuously during sexual contacts. The most common STDs were reported genital warts, 107 patients (56.3%), vaginal discharge (28, 14.7%), and genital ulcer (33, 17.4%). Two (1%) patients were positive for HIV at the first visit. CONCLUSIONS Patients with STDs should be considered as an important source of HIV transmission, so clinicians should pay more attention to screening these patients for HIV infection.