A histopathologic study on hemosiderin deposition in the pancreas was performed. This study included three patients with primary hemochromatosis and 25 patients with aplastic anemia who were receiving blood transfusions. In the three patients with primary hemochromatosis, hemosiderin deposition was present in the acinar tissue, interstitium, islets of Langerhans, and ductal epithelium but occurred predominantly in the acinar tissue. Fibrosis was also found in the interlobular and intralobular areas in a diffuse and irregular manner. A micronodular arrangement of the acinar tissue was present in the atrophic exocrine pancreas. In patients with aplastic anemia who were receiving blood transfusions, the distribution and the quantity of hemosiderin approximately increased in accordance with the volume of blood given. Atrophy of the acinar tissue, interstitial fibrosis, and micronodular formation in the exocrine pancreas occurred in those patients who received a large volume of blood. Therefore, micronodular formation in the exocrine pancreas was one of the characteristic findings in patients with primary hemochromatosis and in patients with aplastic anemia who had received blood transfusions over a long period.