Prokaryotic pathogens have developed specialized mechanisms for efficient uptake of ferrous iron (Fe2+) from the host. In Legionella pneumophila, the causative agent of Legionnaires' disease, the transmembrane GTPase FeoB plays a key role in Fe2+ acquisition and virulence. FeoB consists of a membrane-embedded core and an N-terminal, cytosolic region (NFeoB). Here, we report the crystal structure of NFeoB from L. pneumophila, revealing a monomeric protein comprising two separate domains with GTPase and guanine-nucleotide dissociation inhibitor (GDI) functions. The GDI domain displays a novel fold, whereas the overall structure of the GTPase domain resembles that of known G domains but is in the rarely observed nucleotide-free state.