We have previously conducted clinical trials of allogeneic hematopoietic SCT with reduced-intensity conditioning regimen (RIC) for adult T-cell leukemia/lymphoma (ATLL)-a disease caused by human T-lymphotropic virus type 1 (HTLV-1) infection and having a dismal prognosis. Long-term follow-up studies of these trials revealed that 10 of the 29 patients have survived for a median of 82 months (range, 54-100 months) after RIC, indicating a possible curability of the disease by RIC. However, we have also observed that the patterns of post-RIC changes in HTLV-1 proviral load over time among the 10 survivors were classified into three patterns. This is the first report to clarify the long-term outcomes after RIC for ATLL patients.