Recent reports state that prolonged gallbladder opacification after an otherwise normal oral cholecystogram is abnormal and reliably indicates acalculous cholecystitis. In 122 patients on a variety of diets, the frequency with which prolonged gallbladder opacification is detectable one and two days after oral cholecystography was studied prospectively. Prolonged opacification was seen in 75% of patients and did not occur more commonly in those patients with documented gallbladder disease. Prolongation of gallbladder opacification after oral cholecystography is common and cannot be used as the sole criterion for the diagnosis of cholecystitis.