Purpose To analyze the outcome, including nonrelapse mortality (NRM), relapse rate (RR), progression-free survival (PFS), and overall survival (OS), of patients with diffuse large B-cell non-Hodgkin's lymphoma (DLBCL) relapsed after an autologous stem-cell transplantation (ASCT) and treated with an allogeneic stem-cell transplantation (allo-SCT). Patients and Methods The European Group for Blood and Marrow Transplantation database was scanned for a first allo-SCT in relapsed DLBCL after a previous ASCT between 1997 and 2006. Other inclusion criteria were age at allo-SCT >= 18 years and availability of an HLA-identical sibling or a matched unrelated donor. A total of 101 patients (57 males; median age, 46 years) were included. Median follow-up for survivors was 36 months. Results Myeloablative conditioning regimen was used in 37 patients and reduced intensity conditioning (RIC) was used in 64 patients. Three-year NRM was 28.2% (95% CI, 20% to 39%), RR was 30.1% (95% CI, 22% to 41%), PFS was 41.7% (95% CI, 32% to 52%), and OS was 53.8% (95% CI, 44% to 64%). NRM was significantly increased in patients >= 45 years (P = .01) and in those with an early relapse (<12 months) after ASCT (P = .01). RR was significantly higher in refractory patients (P = .03). A time interval to relapse after ASCT of <12 months was associated with lower PFS (P = .03). The use of RIC regimens was followed by a trend to a lower NRM (P = .1) and a trend to a higher RR (P = .1), with no differences in PFS and OS. No differences were seen between HLA-identical siblings and matched unrelated donors. Conclusion Allo-SCT in relapsed DLBCL after ASCT is a promising therapeutic modality. Patients with a long remission after ASCT and with sensitive disease at allo-SCT are the best candidates for this approach. J Clin Oncol 29: 1342-1348.