Background: Lung cancer remains the leading cause of cancer-related deaths in the world. In Iran, lung cancer is the fifth leading cancer and its prevalence rate has been increasing steadily. In this study, the clinicopathological aspects of lung cancer are discussed. Materials and Methods: Between October 2002 and November 2005, 242 (178 men, 64 women) patients with histologically confirmed lung cancer were interviewed according to a questionnaire. Results: Women developed the disease at an earlier age than men (55.9±14.2 versus 61.3±12.3 years; p=0.004); 66.5% of lung cancer patients (85.4% of men and 14.1% of women) were smokers (p <0.0001); 76.3% of participants, who had exposure to secondhand smoke, were females. Among the environmental carcinogens, the most exposures were to inorganic dusts (49.8%) and chemical compounds (34.9%).Most male and female patients suffered from adenocarcinoma (28.9%) and non small cell carcinoma (28.5%). The prevalence of adenocarcinoma was higher in the non-smoker group, whereas incidence of squamous cell carcinoma and small cell carcinoma was higher among smokers (p <0.0001). In this study, most patients (74.0%) presented with an advanced-stage tumor (IIIB or IV). Conclusion: Our results suggest that in addition to cigarette smoking, other environmental, occupational and socioeconomic factors may play a role in the development of lung cancer. (Tanaffos 2009; 8(3): 28-36)