Lung cancer is a disease of uncontrolled cell growth in tissues of the lung. This growth may lead to metastasis, which is invasion of adjacent tissue and infiltration beyond the lungs. The vast majority of primary lung cancers are carcinomas of the lung, derived from epithelial cells. Lung cancer is the leading cause of cancer deaths in developed countries and is also rising at alarming rates in developing countries. Deaths due to lung cancer are more than those due to colorectal, breast and prostate cancers put together. Incidence and mortality from lung cancer in females is rising while it is declining in males in developed countries. Lung cancer is the single most devastating cause of cancer–related deaths. This cancer is responsible for about one million deaths per year at present and it will rise to three million per year by the year 2010. The worldwide incidence is 14% whereas it constitutes 6.8% of all cancers in India. It is the leading cancer of both sexes in three of the Urban Cancer Registries (Bhopal, Delhi and Mumbai) in India.