Yttrium 90-labeled ibritumomab tiuxetan is approved for the treatment of patients with relapsed or refractory low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma (NHL). To date, the efficacy of repeated courses of radioimmunoconjugate treatment in patients whose disease has progressed has not been studied as a formal endpoint in a clinical trial setting. However, several clinical studies have been conducted in patients with progressive NHL who had previously received 90Y ibritumomab tiuxetan. A retrospective review of these studies has shown that clinical responses have been achieved with all types of subsequent treatment with no apparent impact on their efficacy. In addition, no significant differences in toxicities with subsequent therapies have been observed between patients who had previously received 90Y ibritumomab tiuxetan therapy and those who had not. These findings suggest that patients previously treated with 90Y ibritumomab tiuxetan can feasibly undergo other forms of treatment for progressive NHL, and that a clinical response to further treatment options is not precluded by administration of 90Y ibritumomab tiuxetan.