OBJECTIVE To evaluate the relationship between clinical information (including age, laboratory data, and sonographic findings) and severe complications, such as gangrene, perforation, or abscess, in patients with acute acalculous cholecystitis (AAC). METHODS The medical records of patients hospitalized from January 1997 to December 2002 with a diagnosis of acute cholecystitis were retrospectively reviewed to find those with AAC, confirmed at operation or by histologic examination. Data collected included age, sex, white blood cell count, AST, total bilirubin, alkaline phosphatase, bacteriology, mortality, and sonographic findings. The sonographic findings were recorded on a 3-point scale with 1 point each for gallbladder distention, gallbladder wall thickness >3.5 mm, and sludge. The patients were divided into 2 groups based on the presence (group A) or absence (group B) of severe gallbladder complications, defined as perforation, gangrene, or abscess. RESULTS There were 52 cases of AAC, accounting for 3.7% of all cases of acute cholecystitis. Males predominated. Most patients were diagnosed by ultrasonography (48 of 52) or computed tomography (17 of 52). Severe gallbladder complications were present in 27 patients (52%, group A) and absent in 25 (group B). Six patients died with a mortality of 12%. Four of the 6 who died were in group A. Patients in group A were significantly older than those in group B (mean 60.88 y vs. 54.12 y, P=0.04) and had a significantly higher white blood cell count (mean 15,885.19 vs. 9,948.40, P=0.0005). All the 6 patients who died had normal white blood cell counts with an elevated percentage of band forms. The most commonly cultured bacteria in both blood and bile were E. coli and Klebsiella pneumoniae. The cumulative sonographic points did not reliably distinguish between groups A and B, even though group A tended to have more points. CONCLUSIONS Older patients with a high white cell count are more likely to have severe gallbladder complications. In these patients, earlier surgical intervention should be considered if the sonographic findings support the diagnosis of AAC.