BACKGROUND: Acute acalculous cholecystitis (AAC) is a serious complication of critical illness. We evaluated the underlying diseases, clinical and diagnostic features, severity of associated organ failures, and outcome of operatively treated AAC in a mixed ICU patient population. METHODS: The data of all ICU patients who had operatively confirmed AAC during their ICU stay between 1 January 2000 and 31 December 2001 were collected from the hospital records and the intensive care unit's data management system for predetermined variables. RESULTS: Thirty-nine (1%) out of 3984 patients underwent open cholecystectomy for AAC during the two-year period. Infection was the most common admission diagnosis, followed by cardiovascular surgery. The mean APACHE II score on admission was 25, and 64% of the patients had three or more failing organs on the day of cholecystectomy. The mean length of ICU stay before cholecystectomy was 8 days, and the mean total length of ICU stay was 19 days. Most patients (85%) received norepinephrine infusion, and 90% suffered respiratory failure before cholecystectomy. Hospital mortality was 44%. The non-survivors had higher Sequential Organ Failure Assessment (SOFA) scores on the day of cholecystectomy compared to the survivors (12.9 vs. 9.5, P = 0.007). CONCLUSION: Acute acalculous cholecystitis was associated with severe illness, infection, long ICU stay, and multiple organ failure. Mortality was related to the degree of organ failure. Prompt diagnosis and active treatment of AAC can be life-saving in these patients.