Bartonellae are arthropod-borne bacterial pathogens that typically cause persistent infection of erythrocytes and endothelial cells in their mammalian hosts. In human infection, these host-cell interactions result in a broad range of clinical manifestations. Most remarkably, bartonellae can trigger massive proliferation of endothelial cells, leading to vascular tumour formation. The recent availability of infection models and bacterial molecular genetic techniques has fostered research on the pathogenesis of the bartonellae and has advanced our understanding of the virulence mechanisms that underlie the host-cell tropism, the subversion of host-cell functions during bacterial persistence, as well as the formation of vascular tumours by these intriguing pathogens.