Lung cancer is the most common fatal malignancy in both men and women, both in the United States and elsewhere in the world. Today, lung cancer is most often diagnosed on the basis of symptoms of advanced disease or when chest x-rays are taken for a variety of purposes unrelated to lung cancer detection. Unfortunately, in the United States no society or governmental agency recommends screening, even for patients with high risks, such as smokers with airflow obstruction or people with occupational exposures, including asbestos. The origins of this negative attitude toward lung cancer screening are found in 3 studies sponsored by the National Cancer Institute in the mid-1970s and conducted at Johns Hopkins University School of Medicine, the Mayo Clinic, and the Memorial Sloan-Kettering Center. These studies concluded that early identification of lung cancer through chest x-rays and cytologic diagnosis of sputum did not alter disease-specific mortality. However, patients with earlier stage disease were found through screening, which resulted in a higher resectability rate and improved survival in the screening group compared with a control group of patients receiving ordinary care. Patients in the control group often received annual chest x-rays during the course of this study, which was the standard of care at the time. Thus no true nonscreening control group resulted. The patients at highest risk were not enrolled in this study. No specific amount of pack-years of smoking intensity was required. Only men were screened. The studies were inadequately powered to show an improvement in mortality rate of less than 50%. Ninety percent of lung cancer occurs in smokers. The prevalence of lung cancer is 4 to 6 times greater when smokers have airflow obstruction than with normal airflow, when all other background factors, including smoking history, occupational risk, and family history, are the same. Screening heavy smokers (ie, > or = 30 pack-years) with airflow obstruction (forced expiratory volume in one second < 70% of normal) will yield 2% or more patients with lung cancer (prevalence cases) and, over the course of 5 years, probably from 2% to 3% of patients with additional cancers, yielding an overall incidence of 5%. New technologies include low-dose helical computed tomographic scans for small peripheral adenocarcinomas that cannot yet be visualized by standard chest x-rays and cytologic diagnosis of sputum for central squamous cell lesions. These tests are complementary. A new health care initiative, the National Lung Health Education Program, recommends spirometric testing for all smokers 45 years or older, as well as for patients with symptoms of lung cancer. Screening for lung cancer in such patients will find many cancers at an early stage when they are amenable to cure. Today, we have the knowledge and the technology that could change the outcome of lung cancer.