Acute acalculous cholecystitis is uncommon, accounting for 2-12% of cases of acute cholecystitis. The aetiology remains unknown and may be multifactorial. Most observations of acute acalculous cholecystitis have been recorded in patients after trauma, after unrelated surgical treatment and in critically ill patients. A significant number of cases of acute acalculous cholecystitis occur with no obvious cause. This report notes acute acalculous cholecystitis, diagnosed in 16 patients from 1970 to 1990. The signs and symptoms did not differ markedly from those found when acute cholecystitis is associated with cholelithiasis. Pain and tenderness in the right upper abdominal quadrant, fever, vomiting, jaundice were common. All patients underwent cholecystectomy. Nine gallbladder specimens (56%) had focal gangrene and perforation occurred in 7 instances (44%). Nine patients (56%) developed biliary peritonitis. Bacteria were cultured from 13 of 16 bile specimens. E. coli was the most common organism (69%). A 31% morbidity rate and 25% mortality rate was observed. The etiology and pathogenetic mechanisms acalculous cholecystitis are discussed.