Gastrointestinal graft-versus-host disease (GVHD) is one of the main causes of therapy-related death after allogeneic hemopoietic stem cell transplantation. Early diagnosis and immediate treatment are probably essential for improving clinical outcome. High-resolution sonography allows the evaluation of single bowel wall layers throughout the small and large bowel. We report the sonographic findings of seven consecutive patients with histologically confirmed GVHD grade II-IV of the gastrointestinal tract. The patients were examined sonographically within the 1st week after onset of clinical symptoms. Dilatation of the colon and striking bowel wall thickening were early and common features in these patients. Sonography may become a useful tool for diagnosis of patients with gastrointestinal GVHD. Its role for preclinical diagnosis, grading of severity of disease, and guiding therapy of patients with gastrointestinal GVHD warrants evaluation in prospective studies.