Aim To evaluate the CD8+CD28- and CD4+CD25+ regulatory T (Treg) cells in addition to other some lymphocyte subgroups in peripheral blood of advanced stage lung cancer patients. Methods The study group (n = 28) comprised chemotherapy and radiotherapy naive patients with non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). The control group (n = 22) consisted of age- and sex-matched healthy volunteers. Flow cytometry was used to count T cells, natural killer (NK) cells and CD4+CD25 Treg cells, and for CD8+ T cell subgroup analysis. Flow cytometry was performed and annexin V binding was used for apoptotic cell evaluation. Results In patient group, the percentage of CD8+CD28- cells among lymphocytes was elevated, and there was also an increase in the CD28-/CD28+ cell ratio among CD8 lymphocyte population. The distribution of CD8 cells was different in lung cancer patients when compared with the control group. The absolute count of CD4+CD25(bright) cells and the percentages of these cells among total lymphocytes were higher in the patient group. The Annexin V(+) cell percentages among CD8+CD28- and CD8+CD28+ lymphocytes were higher in the patient group than in the control group. No differences were found between the NSCLC and SCLC patients with respect to the hematological parameters and the distribution of lymphocyte subgroups. In NSCLC patients, the percentage of CD8+ CD28- cells among the lymphocyte population was higher in patients with stage IV than those with stage III. Conclusion These findings may reflect the possibility of tumor-induced immunosuppression and they should be complemented with further studies.