Color velocity imaging is a color sonographic technique that uses data contained in gray-scale B-mode image scan lines to determine blood flow velocity. We prospectively determined if color velocity imaging and power Doppler sonography can be used to differentiate acute from chronic cholecystitis. We analyzed the potential role of using these two color imaging techniques as an adjunct to conventional gray-scale sonography to differentiate acute from chronic cholecystitis. One hundred twenty-nine patients with acute right upper quadrant pain or clinically suspected cholecystitis underwent color velocity imaging and power Doppler sonography of the gallbladder as an adjunct to gray-scale sonography. Morphologic criteria were analyzed on gray-scale sonography, and the presence of flow within the gallbladder wall was assessed with color velocity imaging and power Doppler sonography. Imaging findings were compared with pathologic findings in the 50 patients who underwent cholecystectomy and with clinical and biologic findings in the 79 patients who did not undergo cholecystectomy. Twenty-two patients had surgically proven acute cholecystitis, 28 patients had surgically proven chronic cholecystitis, and 79 patients had no gallbladder disease. Sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of gray-scale sonography for revealing acute cholecystitis were 86%, 99%, 92%, 87%, and 97%, respectively. Sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of color velocity imaging and power Doppler sonography for revealing acute cholecystitis were 95%, 100%, 99%, 100%, and 99%, respectively. The accuracy of color velocity imaging and power Doppler sonography in revealing acute cholecystitis is significantly greater than the accuracy of gray-scale sonography.