Diabetes mellitus is found with increased frequency in patients with both primary and secondary hemochromatosis. In these conditions, the pancreas shows fibrosis and iron overload of acini, interstitium, and islet B cells. Previous morphological studies have only described changes found in advanced stages of disease, while abnormalities of the initial stage of iron overload have, as yet, not been reported. Rats fed a carbonyl iron‐supplemented diet for 4–15 months showed storage iron deposition (ferritin and hemosiderin) in many organs, in a pattern similar to primary human hemochromatosis. Electron microscopic examination of the pancreas showed ferritin particles segregated in lysosomes of acinar cells, as well as diffuse cytosiderosis of macrophages in the interstitial septa. In the islets, iron deposits were discrete and only in B cells. In the absence of electron‐microscopic studies of incipient pancreatic cytosiderosis in human subjects, the present experimental animal study may contribute to a better understanding of the pathway leading to the extensive lesions found in the advanced stages of the human iron overloading diseases.