['Once gastrointestinal (GI) graft-versus-host disease (GVHD) occurs after hematopoietic stem cell transplantation, it may be life-threatening. Therefore, an earlier accurate diagnosis of macroscopic and microscopic features using an appropriate modality improves the prognosis of patients with suspected GI-GVHD.', 'In patients experiencing watery diarrhea within 100 days after hematopoietic stem cell transplantation, we evaluated the severity of mucosal injury at the proximal ileum, terminal ileum, and rectum according to previously reported criteria using transanal single balloon endoscopy. GI-GVHD was diagnosed by the presence of gland apoptosis without inflammatory or infectious factors in the biopsied specimens obtained from their respective site regardless of the mucosal lesion.', 'Consecutive suspected GI-GVHD patients with watery diarrhea (11 men and 5 women, mean age: 45.6 years, coexistent symptoms: nausea [38%] and exanthema [69%]) were enrolled. GI-GVHD was identified pathologically in 11 patients (69%), all of whom had pathological findings of GI-GVHD at the rectum. However, eight patients (73%) had pathological findings of GI-GVHD at both the ileum and the rectum and none had pathological findings of GI-GVHD at the ileum alone. The accuracies for a pathological diagnosis of GI-GVHD based on endoscopic features were 44%, 44%, and 38% at the proximal ileum, terminal ileum, and rectum, respectively. The severity of mucosal injury had no association with the diagnostic rate of pathological GI-GVHD at any site.'] Is rectal biopsy , rather than ileal , appropriate to confirm the diagnosis of early gastrointestinal graft-versus-host disease?