The development of acute cholecystitis in the ICU is now a well-recognized complication of many acute illnesses that precipitate ICU admission and may also result as a complication of the subsequent treatment. The etiology of the disease remains obscure and, unlike acute cholecystitis outside the ICU setting, most cases are acalculous and not associated with gallstones. The disease may often go unrecognized due to the complexity of the patient's medical and surgical problems. Clinical examination is often unhelpful, as many patients are receiving mechanical ventilation and have decreased mental awareness. Biochemical markers are nonspecific and contribute to the delay in diagnosis and treatment. Early diagnosis is essential to avoid the high rates of associated morbidity and mortality. The diagnosis is usually made by radiologic tests, most often by sonographic examination of the gallbladder, which can be performed at the bedside. However, radiologic findings may also be nonspecific. The treatment involves gallbladder drainage by percutaneous cholecystostomy, which is usually curative in acalculous cholecystitis. Interval cholecystectomy is indicated for the remaining patients with gallstone-associated cholecystitis.