For a period of 23 years, from 1919 until 1941, 25 cases of primary lung carcinoma have been observed amongst the total number of 6.458 post mortem examinations, registered at the Section of Pathological Anatomy of the Osvaldo Cruz Institute and performed at various hospitals of Rio de Janeiro. The individuals were of varying descent, not only from different Brasilian regions, but also from several foreign countries. The incidence of primary lung carcinoma, considered as causa mortis, amongst the total number of necropsies is 0,38 % and amongst the cases of cancer, 4,5 %. As to sex, 21 cases are male (84 %) and 4 of female individuals (16 %), giving the ratio of 5:1. Out of the 25 cases, 13 (52 %) were aliens and 12 (48 %) of Brasilian nationality; 18 in individuals of white, 6 of black colour and 1 in a mulatto. As to age, the largest incidence ocurred between 51 and 60, there being also extreme cases with 21 and 93 years. The most frequent anatomical form, in the same material, is the infiltrating hilar, 16 cases (64 %), folowed by the nodular form with 7 cases (28 %) and by the diffused one in 2 cases (8 %). The undifferenciated cell carcinoma is the most commonly met with, observed in 13 cases (52 %), followed by that of cylindrical cell in 8 cases (32 %) and by that of squamous cell in 4 cases (16 %) . Incidence of metastasis was observed in 22 cases (88 %): 76,9 % for the undifferenciated cell carcinoma, and 100 % for each of the other two, either of cylindrical or of squamous cells. In 3 cases (12 %) no metastasis was observed. As to the organs, which are the frequent seat of metastasis, the following order was observed: lymph nodes, 72 %; liver, 56 %; pleura, 12 %; peritoneum, pericardium, kidney and suprarrenals, 8 %; brain and bone, 4 %. In the last 10 years (1932 until 1941) 16 cases occurred (64 % of the total number 25) showing, if not an increase of lung cancer, certainly a larger number of positive diagnosis.