Background: Lung cancer is the most common neoplasm in Turkey, but there is not enough data on the characteristics of this mortal illness in our country. Objectives and Methods: The Turkish Thoracic Society, Lung and Pleural Malignancies Study Group (TTS-LPMSG) conducted a national retrospective hospital-based study to determine the pattern of lung cancer in Turkey. Results: A total of 11,849 lung cancer patients were studied between 1994 and 1998, 90.4% were male and 9.6% were female. The majority of patients were smokers (77.9%) or ex-smokers (10.8%). The mean age at the time of diagnosis was 58.4 years (20-84) and 56.7% of the patients were aged between 46 and 65 years. The most common histological types were squamous cell (45.4%), small cell (SCLC; 20.5%) and adenocarcinoma (20.2%). The majority of patients with non-small-cell lung cancer were diagnosed with metastatic disease (40.4%). Of the patients with SCLC patients, 37.9% had limited stage disease and 62.7% extensive stage disease at diagnosis. Conclusion: The results of the largest data so far collected in Turkey show that the vast majority of patients with lung cancer are male, squamous cell is the most common histological type, and only a small proportion of patients are diagnosed at an early stage. Copyright (C) 2002 S. Karger AG, Basel.