Background: Individuals that are HIV positive can transmit the infection through unprotected sex. Objectives: The present study aimed to evaluate the prevalence and determinants of consistent condom use among Iranian people living with HIV/AIDS as one of the most stigmatized and hard-to-access groups in this country. Patients and Methods: This cross-sectional study was conducted in Tehran, Iran. A total of 400 heterosexuals living with HIV/AIDS were sampled from 5 behavioral consulting centers through a purposive sampling method. Data were collected through an interviewer-administered questionnaire. Bivariate logistic regression, chi-square test, and multivariate logistic regression model were used as the statistical models in this study. Results: Of all 400 participants, 240 (60%) were men. The mean age was 34.7 for both sexes. During the past year, 335 (83.7%) were sexually active and 269 (67.9%) reported never having used a condom. Consistent condom use (always using condom in sexual intercourse) was reported by 67 (16.7%) of the participants. Consistent condom use was significantly associated with participation in HIV prevention courses (P = 0.003), knowledge of unsafe sex consequences (P = 0.017), condom use as a dual protection method (P = 0.0001), having a HIV-positive sexual partner (P = 0.0001), as well as being in a regular sexual relationship (P = 0.005). Conclusions: Development and improvement of the HIV prevention programs seems necessary to control the transmission of HIV in each community. However, results of the present study emphasize the importance of more attention to some specific programs such as prevention of mother-to-child transmission as a result of the willingness of Iranian people living with HIV/AIDS to child bearing. In addition, more attention should be paid to women as the more vulnerable part of the community to better prevent and control HIV in Iran.