A 46-yr-old man with cirrhosis presented with mental confusion, headache, and nausea. Colloid liver scintigraphy showed a defect in the hilar area, and portograms after superior mesenteric arteriography demonstrated varicose veins in the same area. Computed tomography revealed a sausage-shaped low-density channel connecting the hepatic hilum and the inferior vena cava, and bolus injection contrast enhancement demonstrated transit of contrast medium from the portal vein directly into the inferior vena cava through this channel. Real-time ultrasound demonstrated a large conduit contiguous from the portal vein to the inferior vena cava through and behind the liver. The catheter introduced into the inferior vena cava opacified a large opening of this shunt below the right and left hepatic vein openings. Measurements of blood pressure, ammonia, and PaO2 clearly indicated that portal vein blood was being shunted through this channel. These findings are highly suggestive of a portosystemic shunt through a patent ductus venosus.