The effects of tobacco smoking on the immunity of HIV-infected patients in the Thai population were studies. The means of absolute CD4+ T lymphocyte count between 22 smoking and 88 non-smoking patients were evaluated and compared using flow cytometry. Results showed that the mean of the absolute CD4+ T lymphocyte count among the HIV-infected smoking group (mean=331 cells/µL) was significantly lower than the HIV-infected non-smoking group (mean=416.19 cells/µL), (P=0.131). The majority of the HIV-infected smokers group still had CD4+ T cell levels lower than 350 cells/µL. Therefore, CD4+ T lymphocytes at the level of 350 cells/µL, according to the treatment guidelines published by WHO, must be maintained. Furthermore, the percentage of CD4+ T lymphocytes in the smoking group was still higher than the non-smoking group.