The gallbladders of 65 patients with ascites were examined on ultrasonograms. In 37 patients, the thickness of the gallbladder wall was less than or equal to 3 mm and was considered normal or "single." In 28 patients, the gallbladder wall thickness was greater than or equal to 4 mm, with a central echo-free zone giving the appearance of a double wall. Of the 37 patients with single-walled gallbladders, 35 (95%) had carcinomatous peritonitis. Of the 28 patients with double-walled gallbladders, 23 (82%) had benign disease, such as liver cirrhosis (n = 22) and nephrotic syndrome with hypoalbuminemia (n = 1). The results of this study indicate that sonography is useful in determining whether the cause of ascites is malignant or benign disease.