Thirty-eight cases of bronchioloalveolar carcinoma were selected on anatomico-pathological criteria and analysed both radioclinically and histologically. At histology, this type of carcinoma is characterized chiefly by the growth of malignant cells along the alveolar walls. Cytology, which determines the nature of these cells (pneumocyte II or Clara cell), is not specific but remains important as regards phylogenesis. The course of bronchioloalveolar carcinoma gives a better understanding of its mode of propagation. Actuarial curves show that all patients with a diffuse carcinoma die very rapidly, whereas the survival rate of those who have localized lesions is 60% at 5 years. Moreover, the time required for dissemination to take place is long in assessable cases. This means that the condition should be diagnosed at an early stage on the presence of crepitant rales, on their air bronchogram at CT and on transparietal needle biopsy under CT. The chances are that early excision will result in cure.