One hundred ten patients with multiple myeloma (MM) failing to achieve at least near-complete remission (nCR) after a first autologous stem cell transplantation (ASCT) were scheduled to receive a second ASCT (85 patients) or a reduced-intensity-conditioning allograft (allo-RIC; 25 patients), depending on the human leukocyte antigen (HLA)-identical sibling donor availability. There was a higher increase in complete remission (CR) rate (40% vs 11%, P = .001) and a trend toward a longer progression-free survival (PFS; median, 31 months vs not reached, P = .08) in favor of allo-RIC. In contrast, it was associated with a trend toward a higher transplantation-related mortality (16% vs 5%, P = .07), a 66% chance of chronic graft-versus-host disease and no statistical difference in event-free survival and overall survival. Although the PFS plateau observed with allo-RIC is very encouraging, this procedure is associated with high morbidity and mortality, and therefore it should still be considered investigational and restricted to well-designed prospective clinical trials. This trial is registered at ClinicalTrials.gov ID number NCT00560053.