Background. The aim of the study was to evaluate the incidence of atelectasis and predisposing risk factors in patients operated for non‑small cell lung cancer. Material and methods. The authors retrospectively analyzed 67 medical histories of patients who underwent lobectomy, segmentectomy and bilobectomy in the Military Medical Academy University Teaching Hospital – Central Veterans’ Hospital in 2015. The postoperative atelectasis was determined by chest radiographic reports. It was examined if age, sex, BMI, size and histological type of tumor, type of surgery and preoperative FEV1 have impact on the incidence of atelectasis. Results. In 26 patients postoperative atelectasis was observed, 11 in females and 15 in males. Age, sex, histological type of tumor and tumor size, did not reach values defining the risk of postoperative atelectasis (p <0.05). On the other hand, obesity, preoperative FEV1≤80 and the procedure performed on the left lung were reported to be statistically significant. Conclusions. BMI >30 patients with preoperative FEV1≤80, and those who underwent surgery on their left lung are more susceptible to postoperative complication of atelectasis.