A prospective, multicenter, nonrandomized phase 2 trial was conducted to evaluate the efficacy and safety of a single dose of yttrium-90 ((90)Y) ibritumomab tiuxetan in elderly patients in first relapsed or primary refractory diffuse large B-cell lymphoma (DLBCL) ineligible for stem-cell transplantation. Patients had been previously treated with chemotherapy (group A, n = 76) or chemotherapy plus rituximab (group B, n = 28). Patients in group A were further divided into patients in whom induction therapy had failed (stratum AI, n = 33) and patients who had relapsed after achieving complete response (CR; stratum AII, n = 43). The overall response rate (ORR) was 52% and 53% in strata AI and AII, respectively, and 19% in group B, with CR/CRu rates of 24%, 39.5%, and 12%, respectively. Median progression-free survival was 5.9 months and 3.5 months in strata AI and AII, respectively, and 1.6 months in group B. Median overall survival was 21.4, 22.4, and 4.6 months in stratum AI, stratum AII, and group B, respectively. Two patients died from thrombocytopenic cerebral bleeding following administration of therapy. Nonhematologic adverse events were mild to moderate. (90)Y-ibritumomab is active in patients with relapsed and refractory diffuse large B-cell lymphoma (DLBCL) and its further evaluation in phase 3 studies is ongoing.