Acute acalculous cholecystitis developed in 16 of 92 patients with acute renal failure who had no prior or coincidental biliary tract disease. The cause of this complication is considered to be multifactorial. Risk factors include sepsis, previous surgery, trauma, total parential nutrition, intermittent positive pressure ventilation, opiate sedation, multiple transfusions and hypotension. One patient had 5 risk factors, 15 had 6 or more. Diagnosis was based on clinical suspicion, serial ultrasound scanning and serial estimations of white cell count, liver function and C-reactive protein. Four patients were treated conservatively with antibiotics and ultrasound observation, 10 underwent cholecystotomy and 2 patients had cholecystectomy. Eleven patients survived (69% survival). No patient treated by cholecystotomy required further surgery to the biliary tract. Acute acalculous cholecystitis has become a significant complication in our "high risk" acute renal failure population as intensive care has advanced and patients are surviving longer. Prompt and appropriate treatment will prevent it contributing significantly to the already high mortality of acute renal failure. Anticipation is the watchword.