Ferritin plays a central role in iron metabolism by acting both as iron storage and detoxifying protein. We have generated a ferritin H allele with loxP sites and studied the conditional ferritin H deletion in adult mice. Ten days after Mx-Cre induced deletion, ferritin H mRNA was below 5% in the liver, spleen and bone marrow of deleted mice compared to control littermates. Mice lost their cellular iron stores indicating the requirement of ferritin H in iron deposition. Serum iron and transferrin saturation were slightly increased and correlated with a 2-fold increased iver hepcidin 1 mRNA and a reduced duodenal DcytB mRNA level. Under normal iron regimen, deleted mice survived for 2 years without visible disadvantage. Mice fed on a high iron diet prior to ferritin H deletion suffered from severe liver damage. Similarly, ferritin H deleted mouse embryonic fibroblasts showed rapid cell death after exposure to iron salt in the medium. This was reversed by wildtype ferritin H but not by a ferritin H mutant lacking ferroxidase activity. Cell death was preceded by an increase in cytoplasmic free iron, reactive oxygen species, and mitochondrial depolarization. Conclusion: Our results provide evidence that the iron storage function of ferritin plays a major role in preventing iron-mediated cell and tissue damage.