Lung cancer is the commonest cause of death from cancer in both men and women, with approximately 152,000 new cases and 139,000 deaths in 1988. The incidence and mortality rates are increasing rapidly in women. Two main tests have been used to screen for lung cancer: chest roentgenography and sputum cytology. Four recent controlled trials and one case-control study failed, however, to show that screening reduces lung cancer mortality even in high-risk persons (smokers). In the Mayo Lung Project, for example, the lung cancer death rate in high-risk men offered sputum cytology and chest roentgenogram every 4 months was 3.1 per 1000 person-years, compared with 3.0 per 1000 person-years in a control group. Chest roentgenograms and sputum cytology lead to false-positive test results in smokers of approximately 5% and 0.5%, respectively. Because of the lack of evidence of benefit and because of its potential harms and costs, screening for lung cancer is not recommended.