Two patients, a mother and her son, had idiopathic pulmonary hemosiderosis. In the son, the onset was acute and he died of massive hemoptysis. The mother's disorder developed less acutely and the condition improved after temporary respiratory support and massive corticosteroid therapy. This is the first reported instance of idiopathic pulmonary hemosiderosis occurring in more than one member of the same family. The diagnosis of idiopathic pulmonary hemosiderosis depends on compatible clinical and pathologic data and on exclusion of secondary causes of intrapulmonary hemorrhage.