Background: Tuberculosis is still a major health problem around the globe. Better knowledge of different aspects of the disease, including immunology and immuno-pathogenesis, promises better control measures. Studies regarding quantitative and qualitative changes of lymphocytes have developed our knowledge to a great extent. In this study, quantitative deficiencies of lymphocyte sub-populations and their activation markers have been evaluated. Materials and Methods: Following documentation of smear positive pulmonary Tuberculosis in adult patients referred to Massih Daneshvari Hospital, 40 new cases without any other immunodeficiency conditions such as HIV, CRF, etc were randomly selected. Tuberculin skin test (TST) and chest radiography were performed for each case, and flow-cytometry was done from peripheral blood for lymphocyte sub-populations as CD3, CD4, CD8, CD4/CD8 ratio, CD19, CD16+56, and for Lymphocyte activation markers including CD25, CD69 and HLA-DR. Comparison was made with the historical control group in a study in same city, age as well as same flow -cytometry operator and same including & excluding criteria. Statistical analysis of data using Spearman’s rho, Mann- Whitney U, and Asymp. Sig. (2-tailed) was done. Results: 18 cases (45%) were male and 22 (55%) were female .Age distribution had a minimum of 17 and a maximum of 80 with a mean of 44.18 (19.65). Considering flow-cytometric marker correlation’s, HLA-DR had significant relation to age (P=0.002). The ratio of CD4+ cells also had significant relation to CD3, CD16+56 and HLA-DR markers. A significant difference was found only in the total of CD3+ lymphocytes by comparing PPD positive cases (>or =10mm) with PPD negative patients. The ratio of CD4+ was significantly lower than the normal population, and CD8+ was significantly higher comparing to the control population. The CD4/CD8 ratio was also significantly lower than the normal population. Conclusion: Expression of lymphocyte sub-populations during the course of pulmonary Tuberculosis disease showed positive or negative correlation. By comparing lymphocyte sub-populations of TB patients with the control group, it is concluded that CD4+, CD8+, and CD4/CD8 ratio show significant differences that confirm significant quantitative defects in lymphocytes due to tuberculosis disease. (Tanaffos 2002; 1(4): 37-44)