A prospective ultrasound study of gallbladder wall thickness in patients with suspected gallbladder disease was performed over a 9 month period. Gallbladder walls thicker than 3 mm in fasting patients whose gallbladders were wider than 2 cm were considered abnormal. Gallstones were documented by ultrasound in 62 patients, a thickened gallbladder wall was demonstrated in 12 of these. Five patients without cholelithiasis had thick-walled gallbladders and were diagnosed as acalculous cholecystitis.