Pulmonary lymphangiomatosis is a rare clinical and pathological entity which is distinct from lymphangiomyomatosis and from pulmonary lymphangiectasis. We report a case of a 20 year old man with diffuse lymphangiomatosis involving the mediastinum, lungs and retroperitoneum. The patient's intrathoracic lymphangiomatosis produced restrictive and obstructive impairment of his pulmonary function, but did not result in chylothorax or chylopericardium, which are two common manifestations of the disease. The patient's clinical course was remarkable for the concomitant development of chronic disseminated intravascular coagulation (DIC). Lymphangiomatosis involving both the mediastinum and pulmonary parenchyma is rare, and DIC is a very unusual complication of lymphangiomatosis.