Lung cancer still has a big proportion of cancer related deaths inspite of improvements in chemotherapeutic and surgical treatment approaches. It has a strong relationship with tobacco comsumption so that it can be regard as a common health problem. The survival rates of lung cancer at earlier stages are higher than later stages, so it is worth to effort detect lung cancer at an early stages which can cause mortality reduction and survival improvement. Some screening methods were used in screening trials to achieve a satisfactory mortality reduction with increased survival rates. We discussed about the results of important big trials which have different methods and qualities. There are two important screening tools to discuss about including; chest x-ray and low dose computed thomography (CT). Although there were many randomized or non-randomized trials used these tools for screening programs, few studies have enough power and quality to interpret the results. In this review, we discuss about the latest and detailed data of screening trials including, The Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, Mayo Lung Project, The National Lung Screning Trial (NLST), The NELSON trial, The International Early Lung Cancer Action Program (I-ELCAP). Among the results of the trials we discussed about, only screening with low dose CT showed a statistically significant reduction of lung cancer deaths with increased early detection in high risk patients. Of these trials, the NLST which showed 20% mortality reduction in lung cancer and 6.7% mortality reduction from any cause has enough power to achieve this target and this results have affected nearly all of guidelines and recommendations of experts. The results of studies with low dose CT, especially of the NLST, changed thoughts about lung cancer screening. According to these results, the high risk individuals are suggested to be screened with low dose CT by almost experts and societies. In contrast, there should be further evaluations to clarify costs, harm effects of screening with low dose CT programs or related consequence procedures. Smoke cessation is still the most important strategy for reducing the burden of lung cancer, despite the promising results of screening trials.