Small cell lung cancer (SCLC) is a highly malignant tumor which is nearly always metastatic at diagnosis and generally staged as a localized or diffuse disease. The authors compared the capabilities and the advantages of CT with those of chest films in the diagnosis, staging and follow-up of this type of cancer in 54 patients (52 men and 2 women, mean age: 62 years, range: 45 to 79 years). All the patients were submitted to the same examinations 3 months (18 patients), 6 months (6 patients), 9 months (6 patients) and 12 months (2 patients) after radiochemotherapy. Median survival time was 13 months (range: 6-20 months). On staging, radiography showed mediastinal masses (63%), bronchial narrowing (57%), hilar masses (45%), atelectasis (37%), pleural effusion (29%), pericardial thickening and/or effusion (22%), multiple (20%) or single (16%) peripheral masses and tracheal narrowing (2%). CT was more sensitive, chiefly in depicting mediastinal masses (34 cases demonstrated by CT vs 12 by chest films), bronchial narrowing (38 vs 0) and pericardial involvement (12 vs 0); after CT, 12 patients with localized disease on chest films were diagnosed as having diffuse disease. Complete response after therapy, i.e., the total disappearance of all signs and symptoms of disease for 30 days at least, was depicted by CT in 16 patients and by chest films in 9 patients. Partial response-i.e., disease decrease by 50% or more, with no new lesions, for 30 days at least--was depicted by CT in 16 patients and by chest films in 4 patients. Finally, no response or disease progression was depicted by CT in 10 patients and by chest films in 9 patients. To conclude, the presence of mediastinal and hilar masses, with bronchial narrowing, atelectasis, pleural/pericardial involvement, sometimes with a peripheral mass, are strongly suggestive of small cell lung cancer. CT was more sensitive than chest films in the staging of localized and diffuse disease, but it failed nevertheless to improve significantly the diagnosis, prognosis and follow-up of SCLC relative to chest films (p = 0.34).