Lung cancer is a major cause of cancer deaths. It is the uncontrolled growth of the tissues of the lungs. This causes invasion of the adjacent tissue beyond the lungs. Among patients with lung cancer about 87% of men and 85% of women are smokers. This shows the close relation between Smoking and lung cancer . Cigarettes contain about 40 carcinogens like radioisotopes, nitrasamine and benzopyrene. The risk of developing lung cancer is directly proportional to the amount of tobacco inhaled. Nicotine decreases the immunity of the lungs to malignant growth of tissues. But as a person stops smoking, his chances of developing lung cancer steadily decreases over a period of time. When a person smokes, the carcinogenic chemicals in the smoke are deposited into the lungs. The more the person smokes, the more the amount of carcinogenic material inhaled and deposited in the lungs. This causes DNA damage, oxidative stress and inflammation which helps the initiation and growth of tumors. DNA is an important element necessary for the normal functioning of the body. The DNA damage cannot be rectified by the body and hence the cells begin to multiply in an abnormal way and this leads to the formation of a malignant tumor. Lung cancer is not easily detectable at early stages and gets affected rapidly. It also sometimes affects other parts of the body. It is therefore fatal and contributes to the maximum number of deaths due to cancer. Efforts are now put in to detect and cure lung cancer but the best method is still to stop smoking or not initiate smoking at all.