A 35-year-old male, blood group B, Rh(D)+ type, received an allogeneic peripheral blood stem cell (PBSC) transplant after a non-myeloablative regimen of fludarabine and cyclophosphamide for resistant gammadelta cutaneous T-cell lymphoma (CTCL). The donor was his HLA-identical brother, blood group O, Rh(D)+ type. Graft-versus-host disease (GVHD) prophylaxis was performed with cyclosporine alone. On day +8, massive immune hemolysis occurred, followed by acute renal failure. Hemodialysis was performed eight times until recovery of renal function on day +24. The risk of delayed immune hemolysis after non-myeloablative allogeneic PBSC transplantation with minor ABO-incompatibility must be considered.