Acute Cholecystitis is a common disease and it needs to be treated in emergency. In case of complication, surgery is mandatory in 48-72 hours. Ultrasonography (US) is the first diagnostic step in that it allows to identify the signs of major complications, not always visible. Spiral CT identifies complications misdiagnosed at US and allows a correct classification. However, spiral CT is able to depict fluid collections or gas in the wall or in the lumen of the gallbladder or free air in the peritoneum, signs not always depicted by US and which also needs surgical treatment in emergency. If one or more signs of complications are present, CT is mandatory to identify complicated cholecystitis (phlegmonous or empyematous cholecystitis, abscesses, emphysematous, gangrenous, hemorragic or perforated cholecystitis) and to indicate its urgent surgery
