A 20 year-old man, developed severe anemia due to occult pulmonary hemorrhage and was falsely diagnosed as having hemolytic anemia. Subsequently, lung biopsy and BAL (bronchoalveolar lavage) suggested idiopathic pulmonary hemosiderosis. Immunofluorescence stain of renal biopsy and serum assay for AGBMA (Anti glomeruli basal membrane antibody) was positive, although renal function and urinary sediment were normal. This case report illustrates that renal biopsy is an important diagnostic procedure in the investigation of occult alveolar hemorrhage syndromes even if the renal function is normal.