Lymphocyte subsets enumeration is of paramount importance in the management of immunodeficiency disorders such as HIV/AIDS. For better interpretation of laboratory findings, reference intervals must be determined in each population. Because of scarcity of published studies from Iranian population, lymphocyte subsets were enumerated in 142 healthy Iranian men by a single platform flow cytometric method. Mean and 95% confidence interval for CD4+ T cells, CD8+ T cells, CD4/CD8 ratio, B cells, and natural killer cells were 748.8 (351-1207), 409.0 (192-752), 1.96 (0.77-3.70), 238.6 (82-500), and 200.7 (91-393), respectively. We compared our results with other studies and found significant differences with some of them. In conclusion, we endorse determination of lymphocyte subsets reference interval in different populations. (C) 2010 International Society for Advancement of Cytometry