This study was planned to observe prospectively the effects of standard open pulmonary lobectomy on leukocyte subsets and their connection with oncological outcome. Leukocyte subsets from 200 patients undergoing pulmonary lobectomy were analyzed: 151 patients had non-small-cell lung cancer, and 49 had non-malignant diseases. Blood samples were taken for leukocyte flow cytometry before and five, 30 and 60 days after operation. The end points were: observation of postoperative leukocyte subsets that are dynamic in patients with lung cancer vs. patients without malignant disease; correlations between leukocyte subsets trend and disease-free interval or survival; and identification of prognostic factors related to preoperative leukocyte subsets. Lymphocyte counts significantly decreased at five days after lobectomy while monocyte counts increased, and complete recovery of the preoperative leukocyte setting was documented at 30 and 60 days. The patients with lung cancer showed a significant low percentage of human leukocyte antigens on their monocytes before surgery (P=0.0017), followed by a peculiar disarrangement of leukocytes subsets compared with patients without malignant disease at the five-day control point. There was no correlation between leukocyte subset dynamics and disease free interval or survival. This study proves reductions of T-, B and natural killer cells, and the expression of DR on T-lymphocyte after pulmonary lobectomy; oncological patients were significantly less affected by surgery than non-cancer patients.