One hundred ninety-five patients with suspected acute cholecystitis (AC) underwent both hepatobiliary scintigraphy (HBS) and static gray-scale ultrasonography (US) to assess the relative value of each imaging modality in this clinical setting. HBS was performed after the intravenous injection of 5 mCi Tc-99m iprofenin. Abnormal HBS indicative of AC visualized the common bile duct, but not the gallbladder, within 1 to 4 hours after tracer administration. Abnormal US indicative of AC demonstrated cholelithiasis and/or gallbladder wall edema. In this series, HBS surpassed US in sensitivity (98.3% versus 81.4%), specificity (90.2% versus 60.2%), predictive value of an abnormal test (91.4% versus 51.6%), and predictive value of a normal test (100% versus 92%), HBS should be the procedure of choice for the rapid detection of AC.