We did an epidemiologic survey of 30 children in whom idiopathic pulmonary hemosiderosis was diagnosed. Eighteen patients had died; 12 patients were still living. The majority of the cases were diagnosed in between 1962 and 1971, mainly in the spring and fall. Eighty percent of the patient lived in villages, whereas only 30% of the total population resided in the same type of rural area. Only one (5%) of the deceased children lived in the city, whereas four (33%) of the living children were city dwellers. The socioeconomic conditions were poor, and in 50% of the cases continuous exposure to highly toxic insecticides was elicited by history and investigation of housing conditions. The incidence of newly diagnosed cases decreased with the improvement of living conditions and the prohibition of the use of certain insecticides. We believe that environmental factors, perhaps insecticides, may cause idiopathic pulmonary hemosiderosis in genetically predisposed persons. An epidemiologic history and genetic investigation should be included in the evaluation of patients with any disease when the cause is obscure.