Alveolar cancer is the only true cancer of the lung as opposed to the common bronchial cancer. The authors defend this thesis by contesting the excessive usage of the expression bronchiolo-alveolar cancer and by supporting it with 12 original observations together with the literature review. The anatomo-pathological data are reported and discussed in order to analyze the reliability of the observations; diagnosis can vary according to the methods used in comparing the bronchial cytology and the examination of the operation tissue samples; the evolutive back search of observations revealed that out of 9 operated cases with localized involvement, 5 patients were still alive 2 years later. Complementary examinations by scintigraphy with labelled bleomycin were disappointing; this test performed 4 times was only once positive. Data from electron-microscopy and tissue culture seem to point towards a histogenesis from type II pneumocyte.