The diagnostic power of combined cholescintigraphy and ultrasonography was tested in 67 patients suspected of having acute cholecystitis; of these, 42 (63%) had acute cholecystitis. The predictive value of a positive scintigraphy (PVpos) was 95% and that of a negative (PVneg) was 91% (n = 67). The PVpos and PVneg of ultrasonography were 89% and 75%, respectively (n = 54), and these values did not achieve statistical significance when compared with those for scintigraphy. Inconclusive tests were 10% and 11%, respectively, but in no patient were both scintigraphy and ultrasonography inconclusive. PVpos and PVneg of combined scintigraphy and ultrasonography were 100% when the two test results were identical (n = 34). In patients with one test inconclusive or discrepancy between scintigraphy and ultrasonography, PVpos and PVneg were 79% and 67%, respectively (n = 20). The results suggest that in patients suspected of having acute cholecystitis cholescintigraphy should be the first diagnostic procedure performed. If the scintigraphy is positive, additional ultrasonographic detection of gallstones makes the diagnosis almost certain. If one diagnostic modality is inconclusive, the other makes a fair basis for diagnostic and therapeutic decision. In case of discrepancy between ultrasonography and scintigraphy the diagnosis should be reevaluated.