PURPOSE: To evaluate the dimensions of segment 4 of the liver in patients with cirrhosis by using ultrasonography (US). MATERIALS AND METHODS: The transverse diameter of segment 4 was measured in 125 control subjects without liver disease and 167 patients with cirrhosis. The size of segment 4 was measured on oblique subcostal US scans obtained between the left wall of the gallbladder (or the main fissure after cholecystectomy) and the ascending or umbilical portion of the left portal vein at the point where it gives rise to the branch to segment 4. RESULTS: In the control subject group, the mean diameter of segment 4 was 43 mm +/- 8 (standard deviation). In the patient group, the mean diameter of segment 4 was 28 mm +/- 9. The cause or severity of cirrhosis had no influence on the size of segment 4. CONCLUSION: A decreased diameter of segment 4 may be a helpful adjunct sign of cirrhosis in the US investigation of chronic liver disease.