Patients (47) with cholestatic jaundice were evaluated for extrahepatic biliary obstruction by ultrasonic cholangiography and the results verified by contrast cholangiography, celiotomy, or autopsy. Sonograms were evaluated both with (official reading) and without (blind reading) clinical information. By showing dilated bile ducts, sonography correctly diagnosed extrahepatic obstruction in 26 of 30 patients on official reading and 23 of 30 on blind reading. In all 17 patients without extrahepatic obstruction, sonography revealed the absence of dilated bile ducts. Among patients with extrahepatic obstruction, those with larger bile ducts had higher bilirubin concentrations, longer duration of jaundice, and were more reliably detected by sonography. In these patients, 94% with total bilirubin concentration > 10 mg/dl were detected by sonography, while 47% with total bilirubin concentration is recognized < 10 mg/dl were detected. Although the limited sensitivity of sonography in early extrahepatic obstruction is recognized, it remains a valuable screening test in cholestatic jaundice.