A total of 70 cases of cholestatic jaundice have been studied by gray scale ultrasonography in order to evaluate how this technic may be used to differentiate between intra- and extrahepatic cholestasis. In 37 out of 42 patients (88.1%) with jaundice of extrahepatic origin, dilatation of the biliary tree was demonstrated, whereas in all the 28 patients with intrahepatic cholestasis biliary dilatation was clearly excluded. In addition, gallstones in the biliary ducts were detected in 12 out of 20 cases and enlargement of the head of the pancreas (due to carcinoma or chronic pancreatitis) was often correctly diagnosed (nine out of 13 cases). These results suggest that ultrasonography should represent the first step in the diagnostic approach to cholestasis. Information gained from this noninvasive technic should make it possible to correctly plan the more complex investigations (endoscopic retrograde cholangiopancreatography and percutaneous transhepatic cholangiography).