The initial (prevalence) radiologic and cytologic screening for lung cancer in the Mayo Clinic study (Mayo Lung Project) involved 10,933 outpatients. All were men at high risk for lung cancer, but none were suspected of having it when they entered the Mayo Clinic. Screening identified 91 lung cancers (8.3 per 1,000 screened). Nearly two thirds of the prevalence lung cancers were detected by chest roentgenography alone. Half of these cancers were resected. Only a fifth of the cancers were detected by sputum cytologic examination alone; however, all but 1 of these were resected. Compared with a group of lung cancers encountered in contemporary clinical practice at the Mayo Clinic, the prevalence cancers were more than twice as likely to be (1) resectable, (2) postsurgical Stage I or II (AJCC), and (3) associated with survival 5 yr after treatment.