We report pneumatosis cystoides intestinalis in a 10-month-old girl who developed bloody diarrhea following chemotherapy for leukemia. The diagnosis was made only by colonic endoscopic ultrasonography, whereas the abdominal plain radiogram and computed tomography failed to elucidate the diagnosis. She was successfully treated with hyperbaric oxygen therapy. Wider application of endoscopic ultrasonography may lead to the more frequent detection of pneumatosis cystoides intestinalis, currently a rare disorder.