The authors try to define the criteria for the diagnosis of this unusual variety of bronchio pulmonary adenocarcinoma. They studied only 9 patients, 8 of whom had surgery which allowed to make a correlation between X-ray and morphological findings. The pathologist encountered the usual problems in the diagnosis of a primitive tumor since some metastasis have the same macroscopic and microscopic aspect. The relation between the radiographic image and the anatomical findings is emphasised. From a symptomatic and radiological point of view, the most frequent distinction was between the opaque round intra-pulmonary image and the chronic alveolar opacity. Other radiological types occurrence less frequently, such as the nodular or the hollowed type. The authors emphasize the pronostic importance of distinguishing the localized form, with a generally good prognosis following surgery, form the diffused form, which have a very poor prognosis. Even under the best of conditions, a radiological study must be supported by both surgery and pathology to be sure that the tumor in question is, in fact, strictly localized. The histogenesis of bronchio-alveolar carcinoma is briefly discussed in a study of histology and pathology.