Acalculous cholecystitis is an uncommon but potentially fatal complication of prolonged critical illness. Both clinical and biochemical parameters lack sufficient sensitivity and specificity to confidently make the diagnosis preoperatively. Over a 2 year period we have evaluated 16 patients with suspected acute acalculous cholecystitis by CT. Based on CT findings, a positive diagnosis of acalculous cholecystitis was made in seven of these patients and confirmed pathologically in six. Criteria used in reaching the CT diagnosis and potential advantages of CT over other imaging modalities in this clinical context are considered.