Two fatal cases of idiopathic pulmonary hemosiderosis are reported. A review of the literature shows the prognosis of this disease to be, at least in young patients, somewhat better than generally thought. A positive diagnosis in the living patient is possible with the help of certain diagnostic measures which are discussed. Increasing familiarity with the rather typical manifestations of this disorder may lead to the discovery of a larger number of patients who have a mild form of the disease. The value of splenectomy and therapy with adrenocorticotropin and cortisone is still questionable, but further trials are necessary, possibly together with the use of antihistaminic drugs. Intermittent increases in pressure in the pulmonary circulation, due to a defective vasomotor control, appears to be the most likely pathogenetic mechanism but more investigations are needed to arrive at any positive conclusion.