AbstractIn multiple myeloma (MM), allogeneic stem cell transplantation (alloHCT) carries a lower relapse risk than autologous transplantation but a greater transplant‐related mortality. Nonmyeloablative conditioning for allogeneic transplantation (NST) reduces transplant‐related toxicity. Results are encouraging when used during first remission in low‐risk patients, but less‐so in relapsed or refractory disease. This is a single‐center retrospective analysis of 20 previously treated MM patients who underwent NST from matched‐related or matched‐unrelated donors from 2000–2006. Median age was 52.7 years (37.2–68.0). Twenty‐five percent had advanced or high‐risk disease. Eleven still had active disease prior to NST. Conditioning was total body irradiation 200 cGy on a single fraction on day −5, followed by antithymocyte globulin (ATG) 1.5 mg/kg/day and fludarabine 30 mg/m2/day on days −4 to −2. All received immunosuppression, most commonly with oral mycofenylate mofetil and cyclosporine beginning on day −5. At day 100, 50% had achieved complete remission. Transplant‐related mortality was 25%. Median overall survival (OS) was 21.2 months (0.6–90+) and progression‐free survival (PFS) 6.6 months (0.6–90+). Both OS and PFS were 24% at 3 years. OS was significantly greater for patients with age <52 years (median 27 months vs. 7.9 months, P = 0.031), and there was a trend toward greater OS for those with β2 microglobulin <2.5 mg/l (median 27 months vs. 7.7 months, P = 0.08). Donor characteristics and Ig type had no significant effect on survival. These data suggest a benefit of NST in relapsed/refractory MM. Randomized trials must be performed to confirm and further qualify this benefit. Am. J. Hematol., 2010. © 2010 Wiley‐Liss, Inc.