INTRODUCTION: Graft Versus Host Disease (GVHD)is a well known complication of bone marrow transplant. The small bowel is known to be affected by this disorder. The exact extent and nature of the pathological changes in the small bowel is not well appreciated as this is a difficult area to delineate, specifically in this clinically ill population. We have used capsule endoscopy (CE)in 10 patients thus far with this disorder and report the spectrum of findings. METHODS: 7 Patients with acute and 3 with chronic GVHD were referred for evaluation because of abdominal pain and diarrhea. All patients underwent Capsule Endoscopy with the M2A Capsule Endoscope. All studies were reviewed by two experienced capsule endoscopists. In two patients biopsies of the small bowel were obtained at the time of gastroscopy. One patient underwent repeat Capsule Endoscopy after therapy. RESULTS: In five patients with Grade IV acute GVHD there was extensive and severe small bowel pathology involving the majority of the small bowel. Findings included total loss of villi, severe ulcerations, stricturing and spontaneous bleeding. One patient had a entero-enteric fistula visulized by CE. In one patient with Grade IV acute GVHD capsule endoscopy established the diagnosis. In addition, gastric emptying was markedly delayed in two patients. In three of the cases in this group the cecum was not visualized due to either stricturing or disruption of motility. Histological findings when obtained corroborated the CE findings of severe GVHD without evidence of infection. In two patients with Grade III acute GVHD the CE findings were less severe. In 3 patients with moderate chronic GVHD no mucosal disease was identified. The capsule eventually passed in all cases. CONCLUSION:1. CE is safe in GVHD including Grade IV disease. 2. Severe GVHD affects the entire small bowel causing extensive damage with a large spectrum of findings. 3. Gastric motility may be severly impaired and should be considered when undertaking CE. 4. In chronic GVHD the small bowel mucosa is normal even in the presence of GI symptoms. 5. These findings have direct therapeutic implication in the diagnosis and therapy of Bone Marrow Transplant patients.