Bronchial colonization is frequently reported in patients with lung cancer, and has a potential impact on therapeutic management and prognosis. We aimed to prospectively define the prevalence and nature of bronchial colonisation in patients at the time of diagnosing lung cancer.210 consecutive patients with lung cancer underwent a flexible bronchoscopy for lung cancer. The type and frequency of bacterial, mycobacterial and fungal colonisation were analysed and correlated with the patients' and tumours' characteristics.