Autopsy studies of two infants, one a newborn, the other 4 months old, revealed massive amounts of iron in lysosomes of hepatocytes and pancreatic acinar cells. Iron, which had been transported across the placenta, accumulated in the same cell types as in adults with primary and secondary hemochromatosis. Hemosiderin was found in cardiac muscle cells, gastric and intestinal glands, and endocrine and exocrine organs including pituitary, thyroid, adrenals, islets of Langerhans, and sublingual and sweat glands. The liver was the most affected organ and the normal hepatic architecture was replaced by hepatocytes which were arranged in clusters, pseudoacinar structures, and multinucleated giant cells embedded in a collagen matrix. The islets of Langerhans were hyperplastic and hypertrophic. Ten similar cases, in five families, have been described; no patients lived longer than 4 months. Neonatal iron storage disease is clinically and pathologically distinct from Zellweger's cerebrohepatorenal syndrome and hypermethioninemia (tyrosinemia) neonatal diseases in which large stores of iron are present in hepatocytes. No abnormalities in serum iron, ferritin, or transferrin concentrations were detected in five parents of the affected children.