We report results of a retrospective analysis of 44 patients with relapsed and high-risk multiple myeloma (MM) undergoing allogeneic CD34-selected hematopoietic stem cell transplantation (HSCT) from HLA-compatible donors. Patients had multiply relapsed disease including relapse at <15 months after autologous transplantation and most patients (28 of 44; 65%) also had high-risk cytogenetics. Before transplantation, patients received busulfan (.8 mg/kg × 10 doses), melphalan (70 mg/m(2) × 2 days), fludarabine (25 mg/m(2) × 5 days), and rabbit antithymocyte globulin (2.5 mg/kg × 2 days). Patients with 10/10 HLA- matched donors were treated prophylactically with low doses of donor lymphocyte infusions (.5 to 1 × 10(6) CD3(+)/kg) starting 4 to 6 months after CD34-selected HSCT. Acute (grade II to IV) graft-versus-host disease (GVHD) and transplantation-related mortality at 12 months were 2% and 18%, respectively. Chronic GVHD was not observed in any patient. Overall and progression-free survival at 2 years were 54% and 31%, respectively. By multivariate analyses, the outcomes of CD34-selected HSCT were influenced by presence of extramedullary disease, disease status before CD34-selected HSCT, and age. This study demonstrates notable safety and efficacy of CD34-selected HSCT in patients with multiply relapsed MM, including those with high-risk cytogenetics.