Prospective analysis of the efficacy of 99mTc-IDA cholescintigraphy and cholecystosonography showed that both are excellent techniques for assessing patients with suspected acute cholecystitis (accuracy 84.7% and 88.1% respectively). Consequently, the choice of tests selected to evaluate patients with suspected acute cholecystitis depends on several factors including; (a.) quality of equipment available; (b.) capability of the technologist performing the examination; (c.) relative experience of the physician supervising the examination; and (d.) willingness of the surgical consultant to accept a positive examination as sufficient evidence to perform emergency surgery. The authors feel that cholecystosonography should be used to assess the presence of acute cholecystitis in jaundiced patients because of its capability in the assessment of bile duct dilatation, and because of the lower reliability of cholescintigraphy when bile duct obstruction is possible (i.e., in jaundice). Ancillary findings in cholecystosonography and cholescintigraphy can aid in the differential diagnosis of acute right upper quandrant pain syndromes.