Patients with chemotherapy-refractory chronic lymphocytic leukemia (CLL) have a short life expectancy. The aim of this study was to analyze the outcome of patients with advanced CLL when treated with nonmyeloablative conditioning and hematopoietic cell transplantation (HCT). Sixty-four patients diagnosed with advanced CLL were treated with nonmyeloablative conditioning (2 Gy total-body irradiation with n = 53 or without n = 11 fludarabine) and HCT from related (n = 44) or unrelated (n = 20) donors. An adapted form of the Charlson comorbidity index was used to assess pretransplantation comorbidities. Sixty-one of 64 patients had sustained engraftment, whereas three patients rejected their grafts. The incidences of grades 2, 3, and 4 acute and chronic graft-versus-host disease were 39%, 14%, 2%, and 50%, respectively. Three patients who underwent transplantation in complete remission (CR) remained in CR. The overall response rate among 61 patients with measurable disease was 67% (50% CR), whereas 5% had stable disease. All patients with morphologic CR who were tested by polymerase chain reaction (n = 11) achieved negative molecular results, and one of these patients subsequently experienced disease relapse. The 2-year incidence of relapse/progression was 26%, whereas the 2-year relapse and nonrelapse mortalities were 18% and 22%, respectively. Two-year rates of overall and disease-free survivals were 60% and 52%, respectively. Unrelated HCT resulted in higher CR and lower relapse rates than related HCT, suggesting more effective graft-versus-leukemia activity. CLL is susceptible to graft-versus-leukemia effects, and allogeneic HCT after nonmyeloablative conditioning might prolong median survival for patients with advanced CLL.