A prospective study was performed in two parts after sonographic determination of gallbladder wall thickness in 110 consecutive patients. The first part was designed to evaluate accuracy of sonographic measurements in 40 patients on whom intraoperative measurements of wall thickness were obtained. Second, the significance of wall thickness as an indicator of disease was explored by comparing the 40 surgical patients and 44 controls. Sonography was found to be accurate in determining wall thickness to within 1 mm in 93% of patients and 1.5 mm in 100%. Wall thickness greater than 3.5 mm is highly accurate in predicting disease; however, a wall thickness 3 mm or less does not rule out cholecystitis.