To evaluate the usefulness of Courvoisier's sign in ultrasonography, gallbladder size in patients with common hepatic duct dilatation was measured using the ellipsoid method during ultrasonographic examination. During a 6-month period 24 patients with malignant obstructions (6 with carcinoma of the ampulla of Vater, 9 with pancreatic head tumors, 5 with carcinoma of the bile duct, and 4 with malignant lymphadenopathy), 50 patients with calculous obstructions, and a group of 50 normal control patients were examined in this study. Gallbladder volumes were larger in patients with biliary tract dilatation (88.8 +/- 6.8 ml) than in the control group (34.3 +/- 2.8 ml) (p < 0.01). Although the duration and total serum bilirubin level were higher in patients with malignant obstructions, the gallbladder volumes were the same in these two groups (93.0 +/- 11.3 ml versus 86.7 +/- 8.5 ml). A linear relationship was found between gallbladder volume and total serum bilirubin in patients with malignant biliary obstructions (r = 0.6, p < 0.001) and in patients with calculous biliary obstructions without gallbladder stones (r = 0.68, p < 0.001). We hypothesized that the gallbladder volume is irrelevant in differentiating the nature of the biliary tract dilatation and that the gallbladder size is dependent on the degree of biliary obstruction when the gallbladder is not afflicted by fibrosis.