Ferritin is the protein whose function is to store iron that the cell does not require immediately for metabolic processes, thereby protecting against the toxic effects of free Fe(2+). Ferritin therefore plays a crucial role in iron metabolism as well as in the development of some diseases, especially those related to the presence of free Fe(2+) and toxic hydroxyl radicals. In addition, ferritin is itself a catalytic bionanoparticle. Its internal cavity can be used as a nanoreactor to produce non-native metallic nanoparticles. Moreover, its external protein shell can be chemically modified, allowing ferritin to be used as a precursor for a library of metallic nanoparticles, some which may have potential applications in biomedicine, especially as multimodal imaging probes. This article presents a brief overview of the evidence for the role of native ferritin in some diseases, as well as the potential of some synthetic ferritins--in which a non-native inorganic material has been introduced into the cavity and/or the external shell has been modified--in the field of nanobiomedicine.