Acute acalculous cholecystitis (AAC) is a disease that causes high rates of morbidity such as those traditionally observed in the critically ill. Recently we noted an increase in the de novo presentation of outpatients with this disease. Our aim was to characterize this disease in outpatients, identify risk factors, and assess clinical outcome. Therefore a 7-year review of the Yale experience with AAC was undertaken. Forty-seven patients were identified. Seventy-seven per cent (36 of 47 patients) developed AAC at home without evidence of acute illness or trauma, while 23% (11 of 47 patients) developed the disease while hospitalized. Significant vascular disease was observed in 72% of outpatients. A 38% morbidity rate and 6% mortality rate were observed. We conclude that AAC occurs commonly in elderly male outpatients with vascular disease and that these patients incur significant morbidity in association with this condition. AAC should be suspected and prompt surgical management instituted when these patients present with an acute right upper quadrant inflammatory process.