Acute acalculous cholecystitis (AAC) is a well known complication in severely traumatized patients. Existing data of AAC originate from retrospective analyses and episodic case reports. In a prospective study 45 polytraumatized patients admitted to our intensive care unit from January 1989 to June 1990 were clinically and sonographically screened for this condition at defined time intervals. Trauma scoring was performed according to the injury severity score and polytrauma score. AAC was defined as a combination of hydrops of the gallbladder, an increased wall thickness (> 3.5 mm), and the demonstration of sludge. We were able to document this diagnostic triad in 8 (18%) of 45 patients. As a consequence early elective cholecystectomy was performed in 1 of the 8 patients. The remaining patients were treated conservatively. The incidence of AAC in severely traumatized patients is higher than figures so far published suggest. Ultrasound is a reliable method of early detection and follow-up of this complication.