The authors report a new case of pneumoblastoma concerning a 63 years old man who dies with hepatitic insufficiency and massive metastasis. The study in optic and electronic microscopy shows the three cellular contingents which form the pneumoblastoma: clusters of indifferenciated cells, spindle cells and cubic or cylinder epithelial cells, with few secretory granules and microvilli which form tubes or lobules. All the features show clearly a blastematous character very similar to a foetal lung which allows to differenciate the pneumoblastoma from carcinosarcoma.