The aim of the study was to investigate the influence of bacterial colonisation of a neoplastic lung tumour on the frequency of infectious complications after radical surgical treatment of the malignancy.Material and methods. 49 patients operated on for non-small cell lung cancer (NSCLC) from 23rd January to 2nd November 2006 were included into the study. The analyzed group consisted of 39 men and 10 women, they were from 45 to 79 years old. Material for microbiological tests was collected in an operating theatre under sterile conditions directly after the resection of a tumour. A sample (5x5x5 mm) of the tumour was cultured for facultative anaerobes, obligate anaerobes and fungi. After the homogenisation of tumour tissues quantitative culture was also performed.Results. Potentially pathogenic microbes were cultured from tumours in 14 patients (28.6%). The most frequent bacterium was Propionibacterium acnes. It was found in six out of 49 tumours (12.2%). In 13 cases (26.6%) postoperative infectious complications were observed. They were as follows: infection of the lower airways - 8 cases (16.3%), surgical wound infection - 3 cases (6.1%), pleurisy - 1 case (2%) and pleural empyema - 1 case (2%). In 12 patients (24.5%) pathogenic microbes were isolated from biological material obtained from other sources than a tumour. In remaining 36 patients (73.5%) no infectious postoperative complications were observed. In 13 patients in whom bacteria were cultured from a tumour there were no postoperative infectious complications. Only in one patient the same bacterium (Staphylococcus aureus) was identified in a tumour and 35 days later in pleural effusion where four other pathogenic bacteria were isolated, too. In 12 patients whose postoperative course was complicated by infections had no pathogenic microbes cultured from a resected tumour. Statistical analysis showed no significant relations between the presence of pathogenic microbes within a lung malignant tumour and postoperative infectious complications in patients.Conclusions. The most frequent microbe cultured from non-small cell lung carcinoma is Propionibacterium acnes. There is no relation between the colonisation of a malignant tumour by bacteria and postoperative complications in patients treated surgically for NSCLC.