Twenty-one cases of carcinomatous lymphangitis of the lung are reported. In diagnosing them clinical, roentgenologic, and histopathologic criteria were used and the clinical, roentgenologic and evolutive findins were considered in order to emphasize the origin of the primitive neoplasm. From this point of view the principal ones turned out to be carcinomas of the breast, stomach, and lung. The absence of carcinoma of the thyroid gland as a source of pulmonary lymphangitis carcinomatosa must be pointed out. The higher incidence of this condition in older people and the clear predominance in the female sex are stressed. From a clinical standpoint the most important data were the existence of cough and dyspnea, which are often associated with the commom presence of enlarged left supraclavicular or axillary lymph nodes. There was a predominant pure interstitial pattern (the most common feature was the presence of Kerley's A or B lines), sometimes coexisting with alveolar impairment and very often with accompanying pleural effusion. The mean survival rate was 2 months, with a maximum of 7 months and a minimum of 3 days. The results of the present series were compared with those of the literature and the most significant and constant fact in both instances was that two thirds of the cases of pulmonary lymphangitis carcinomatosa had their origin in neoplasms of the breast, stomach, and lung.