Introduction and objective: Lung cancer is diagnosed in most cases at a late stage. Primary diagnosis of patients takes place in pulmonology departments. More effective primary diagnosis through cooperation with thoracic surgery and oncology departments appears to be the key to better treatment outcomes. Objective: The aim of this article was to assess the value of diagnosis performed in the Department of Pulmonology in terms of determining the aetiology and stage of lung cancer and qualifying for thoracic surgical diagnostic and therapeutic procedures. Material and methods: The study included 51 patients with lung cancer detected in imaging tests, who, following a series of diagnostic tests performed in the Department of Pulmonology, e.g. bronchofiberoscopy, fine-needle aspiration biopsy, cytology of the pleural fluid, spirometry, diffusing capacity of the lungs for carbon monoxide, and laboratory tests, were referred to the Department of Thoracic Surgery for radical treatment or complementary invasive diagnosis. Results: The efficacy of pulmonological diagnostic tests in detecting malignancies in the study group was found to be relatively high, with sensitivity of 0.66, specificity of 0.81, and accuracy of 0.71. As a result, radical surgery could be performed in 24 patients (47.06%). Thoracic surgical diagnostic procedures allowed for total lung tumour resection in another 7 patients. In total, 31 patients underwent optimal lung resection (60.78%). Conclusions: Cooperation of the Department of Pulmonology with complementary thoracic surgical diagnostic tests allows for precise determination of the aetiology of lung cancer and implementing ther apeutic surgeries in technically resectable cancers.