Non-Hodgkin's lymphoma (NHL) is the most common hematological malignancy in the United States with a rapidly increasing incidence. Most follicular NHL is indolent but incurable, whereas the more aggressive varieties do respond to therapy. Most patients with follicular NHL who transform to an aggressive NHL are very difficult to treat successfully. Treatment options have included chemotherapy, radiation, immunotherapy with monoclonal antibodies, alone or in combination, and hematopoietic stem cell transplantation. The efficacy of monoclonal antibodies is augmented when they are combined with a radioisotope like iodine-131 or yttrium-90. There have been a number of studies done in recent years studying the efficacy of this form of therapy, i.e., radioimmunotherapy (RIT) in patients with NHL. This review attempts to integrate the information from the various clinical trials done using RIT in patients with relapsed/refractory or newly diagnosed NHL and in hematopoietic stem cell transplantation. It also includes updates on the use of RIT in elderly patients and in patients with significant bone marrow involvement among other recent advances made in this field.