Iron oxide (FeO)-based theranostic agents show great promise toward advancing personalized nanomedicine due to their extraordinary physicochemical and biological properties. This original review aims to highlight and summarize the most recent progress of FeO, starting with the synthesis and surface modification of superparamagnetic iron oxide nanoparticles (NPs). Desirable features of FeO are the initial focus, followed by a review of their theranostic applications including sensitive MRI, multimodal imaging and MRI-guided cancer therapy. Finally, potential nanotoxicity, regulatory and clinical translation barriers are addressed to outline future perspectives on FeO NP-based multifunctional theranostic platforms. It is strongly believed that in the near future, FeO NPs will open new routes with regard to cancer management.