Radioimmunotherapy (RIT) using radiolabeled monoclonal antibodies (MAbs) directed against tumor-associated antigens has evolved from an appealing concept to one of the standard treatment options for patients with non-Hodgkin's lymphoma (NHL). Inefficient localization of radiolabeled MAbs to nonhematological cancers due to various tumor-related factors, however, limits the therapeutic efficacy of RIT in solid tumors. Still, small volume or minimal residual disease has been recognized as a potentially suitable target for radiolabeled antibodies. Several strategies are being explored aimed at improving the targeting of radiolabeled MAbs to solid tumors thus improving their therapeutic efficacy. In this review, various aspects of the application of radiolabeled MAbs as anti-cancer agents are discussed, and the clinical results of RIT in patients with hematological and various solid cancers (colorectal, ovarian, breast and renal carcinomas) are reviewed.