We present here a systematic analysis of lymphoma and MM patients recruited into 2 clinical trials or treated with radretumab according to compassionate use, describing the biodistribution, dosimetry, safety, and clinical activity of radretumab. Methods: Uptake in lymphoma lesions, safety, and clinical activity of radretumab radioimmunotherapy (R-RIT) were evaluated in 18 relapsed lymphoma or multiple myeloma patients. Results: In 14 of 18 patients, selective tumor uptake was found; 11 of 15 lymphoma patients, including 9 of 11 with Hodgkin lymphoma (HL), were eligible for R-RIT (a priori criteria-based target-tobone marrow ratio > 10:1 for EudraCT no. 2005-000545 or > 4:1 for EudraCT no. 2007-007241-12 at dosimetric imaging). Two HL and 1 diffuse large B cell lymphoma patient achieved complete response; 1 HL patient had partial response. Both multiple myeloma patients receiving R-RIT experienced stabilization of disease. Therefore, the overall objective response rate was 40%. Uncomplicated grade 3-4 thrombocytopenia or leukocytopenia was observed in 5 R-RIT patients, lasting 4-129 d. Conclusion: R-RIT showed a favorable benefit and risk profile in advanced relapsed lymphoma patients and induced complete response in 2 heavily pretreated, relapsed HL patients and in 1 diffuse large B cell lymphoma patient. These results warrant further exploration of R-RIT in larger phase II clinical trials. Copyright © 2012 by the Society of Nuclear Medicine, Inc.