We analyzed the results of third allogeneic stem cell transplantation (SCT3) using single-unit unrelated cord blood (CB) in seven adult patients with relapsed acute leukemia after second allogeneic stem cell transplantation (SCT2). The median age at SCT 3 was 44 years (range 20-58 years). The patients had de novo acute myeloid leukemia (AML) (n = 4), secondary AML following myelodysplastic syndrome (n = 2), and acute lymphoblastic leukemia (n = 1). Four patients received myeloablative conditioning, and three received reduced-intensity conditioning. All but one patient had myeloid reconstitution with remission, but five patients relapsed even after SCT3. However, one patient is alive and disease-free 6 years after SCT3, which is the longest remission duration among three allogeneic SCTs she received. Furthermore, actual survival after relapse of SCT 2 was significantly better for patients who received SCT3 compared with institutional control patients who never received SCT3 (P < 0.001). These results suggest that the use of CB may allow the opportunity to perform SCT3 in patients who have experienced relapsed leukemia without donors, and SCT3 with CB may offer the chance of durable remission for selected patients with relapsed acute leukemia.