Oral examination in a patient with a history of acute lymphoblastic leukemia (ALL) and allogeneic hematopoietic cell transplantation (HCT) needs considerations of leukemia relapse and graft-versus-host disease (GVHD). Oral manifestations may contribute to early detection of relapse or systemic complications making accurate oral examination and diagnosis significant. We report a case of a large tumor like mass arising in a patient with a history of ALL and HCT. The patient had been diagnosed with ALL relapse and was being treated with chemotherapy, and furthermore was suspected of GVHD development.