This Phase I/II study investigated myeloablative (131)I-rituximab radioimmunotherapy (RIT) and high-dose chemotherapy supported by one or two autologous stem cell transplantations in heavily pretreated patients with relapsed or refractory B cell non-Hodgkin lymphoma. Myeloablative RIT was safe and feasible when followed by autologous stem cell transplantation with low incidence of secondary late effects and could be a reasonable alternative regimen especially in elderly patients and in patients who have concerns about high-dose chemotherapy. Tandem myeloablative (131)I-rituximab RIT and high-dose chemotherapy supported by two autologous stem cell transplantations was also feasible. However, the toxicity was higher than after myeloablative RIT, therefore it might be recommended to restrict the tandem approach to lymphoma with poor prognosis.