Background: The prediction of postoperative functional status in non-small cell lung cancer patients based on preoperative assessment of physical and respiratory capacity is inadequate based on recent RCTs. Material and methods: Prospectively collected spirometry data and the six-minute walk test results of 57 patients treated with lobectomy for non-small cell lung cancer were analyzed. The tests were performed before surgery, and 30 and 90 days after lobectomy. All patients underwent a respiratory functional and physical capacity assessment. Results: All 57 patients underwent lobectomy. Before surgery, mean FEV1 was 2.4 ± 0.7 L, corresponding to %FEV1 of 88.3 ± 17.3%. The mean absolute and expected 6MWT distance was 548 ± 74.6 m and 108.9 ± 14.5%, respectively. At the first postoperative evaluation 30 days after surgery, FEV1 and %FEV1 decreased significantly by an average of 0.5 ± 0.3 L and 15.1 ± 10.7%, while 6MWT and expected 6MWT decreased minimally by an average of 1.0 m and 0.8%, respectively. Three months after lobectomy, FEV1 and %FEV1, compared with the initial assessment, decreased by an average of 0.3 ± 0.3 l and 7.8 ± 10.0%, while 6MWT and its expected score increased to 564.6 ± 84.6 m and 112.8 ± 15.8%, respectively. Conclusions: After lobectomy, FEV1 decreased slightly and less than expected, while 6MWT increased proportionally compared to the preoperative evaluation.