The diagnostic accuracy of sputum cytology for the diagnosis of bronchial carcinoma using paraffin-embedded, serially sectioned and hematoxylin and eosin-stained specimens was tested in 4,297 sputum samples from 1,889 patients, 219 of whom had bronchial carcinoma. The diagnostic sensitivity depended mainly on the number of investigated samples and was 85.4% with three sufficient sputa. The sensitivity was not influenced by the histologic types, location or TNM stage of the tumor. The specificity of the method was 99.5%. In three cases localization of sputum cytologically diagnosed bronchial carcinomas was not possible immediately (occult carcinomas, pTx); in two of these cases the bronchial carcinomas were located during follow-up. The third patient died without verification of the cytologic diagnosis. According to our results, sputum cytology on serial sections is a valuable instrument for mass screening of high-risk groups for the early detection of bronchial carcinoma. Lower sensitivities of sputum cytology in mass screening programs for the early diagnosis of lung cancer are discussed critically.