The prognosis of patients with poor-risk or relapsed hematological malignancies is dismal. The dose intensification necessary to achieve subsequent CR is limited by the toxicity of chemotherapy. Treatment intensification with double allogeneic HSCT (dHSCT) may enhance the antileukemic effect and reduces treatment-related toxicity associated with prolonged aplasia during reinduction. We evaluated this approach in 23 patients, nine with primary refractory disease or relapse after conventional chemotherapy (group I) and 14 with relapses after allogeneic HSCT (group II). Double HSCT was feasible in all patients. At the end of the observation period, 6 of 23 (26%) patients were still alive and in remission with a median observation time of 60 months (1-153). The overall survival probability at 1 year was 41% (95% confidence interval (CI), 21-62%), transplant-related mortality (TRM) 28% (9-47%) and the incidence of relapse 42% (18-66%). The TRM in groups I and II were 22 and 36% and the relapse rate 33 and 50%, respectively. In conclusion, we have shown the feasibility of dHSCT with an acceptable TRM, irrespective of a previous allogeneic HSCT. Whether this approach offers a survival benefit for patients with poor-risk leukemias has to be tested in larger prospective trials.