Idiopathic retroperitoneal fibrosis (IRF), usually affects the ureter, although the biliary tree, duodenum and vasculature mayalso be susceptible. This case report describes a 64-year-old man with IRF, who presented painless watery diarrhea, radiological features of obstructive jaundice and duodenal obstruction, and ultimately an obstruction of the inferior vena cava. We employed tamoxifen for his treatment, but the disease progressed and the patient died of multiple organ failure two years after the onset. While the cause of IRF in this patient was obscure, we suspected his painless watery diarrhea indicated chronic ischemia of the small bowel, and the findings of an abdominal CTscan were extremely valuable in indicating IRF. (Internal Medicine 42: 812-817, 2003)