A 13-year-old girl with chronic active Epstein-Barr virus (EBV) infection of the γδ T-cell type underwent cord blood transplantation (CBT) 7 months prior to hospitalization. Cord blood (CB) unit assessed for virus safety including EBV was obtained from the CB bank. HLA-DRB1 and HLA-B locus-mismatched CB cells were transplanted into the patient after a preparative regimen consisting of rabbit anti-thymocyte globulin (5.0 mg/kg), fludarabine (180 mg/ m 2 ), melphalan (180 mg/m 2 ), and total body irradiation (4 Gy). The post-CBT course was complicated by gastrointestinal graft versus host disease (GVHD) and recurrent herpes reactivation. The dose of corticosteroid and tacrolimus for GVHD therapy was tapered after GVHD improved but could not be discontinued because her digestive symptoms worsened. Treatment with oral prednisolone (0.15-0.30 mg/kg/d) and tacrolimus (trough concentration 4-6 ng/mL) was necessary for GVHD from 3 months after CBT. Full-donor chimerism was achieved quickly after transplantation and EBV viral load was undetectable in the peripheral whole blood using real-time PCR until 4 months after CBT; viral load increased to 1090-2140 copies/μg DNA at 5 months and 2080-4960 copies/μg DNA at 6 months with full-donor chimerism.Six months after CBT, she presented with swelling of the upper right eyelid, which was resistant to ophthalmological treatments, including antibiotics. Seven months after CBT (1 month after first presentation of symptoms), she was admitted to hospital because of bloody stool with severe abdominal pain in addition to increased swelling of her upper right eyelid (Figure 1A). Orbital computed tomography (CT) revealed a marked thickening of the right conjunctiva, which formed a mass with a maximum diameter of 30 mm (Figure 1B).A drainage incision from the eyelid side was performed, but there was no pus discharge. Endoscopy indicated multiple elevated lesions throughout the stomach, many of which eroded to form ulcers.Pathology revealed significant infiltration of large atypical lymphoid cells in the lamina propria. Immunohistochemical staining disclosed that the atypical lymphoid cells were positive for CD20, CD79a, and Epstein-Barr virus-encoded small RNA-1 in situ hybridization (EBER-ISH) and negative for CD3 and CD56, and ki-67 index up to 73%.