Background and Objective: Anemia is a common manifestation of human immunodeficiency virus (HIV) infection, occurring in approximately 30% of patients with asymptomatic infection and in as many as 75% to 80% of those with AIDS. Anemia has been associated with decreased quality of life and decreased survival. In this study we aimed to determine the prevalence and related factors of anemia in HIV-infected patients. Materials and Methods: A total of 143 HIV positive patients who referred to behavioral disease consulting center in Tehran were screened for anemia. Mild to moderate anemia was defined as hemoglobin (Hb) 8-14g/dl for men and 8-12g/dl for women; severe anemia was defined as Hb less than 8g/dl for both males and females. sociodemographic data were collected using a questionnaire. In all patients, CD4 lymphocytes counting were done by flowcytometry. Results: It was found out that 143 HIV positive patients with a mean age of 37.1+ 2 years were enrolled in our study. The mean Hb level was 13.5 ± 2.1 g/dl. Mild anemia occurred in 46% of subjects while severe anemia was not observed. There was not any significant difference between patients with and without anemia regarding age, gender, stage of the infection, CD4 cells count and concurrent anti-retroviral therapy. We also found significant difference between anemia and risk behaviors for HIV acquisition. Conclusion: Our results showed that mild to moderate anemia was frequent in HIV positive patients but severe anemia was not prevalent in this study population.