Although acute renal failure is a well recognized complication of several extra-hepatic biliary tract diseases especially biliary tract surgery in the presence of obstructive jaundice, there is little information concerning renal failure in acute cholecystitis. Renal function was assessed in 14 patients with acute cholecystitis and two with acute cholangitis. Six patients had no evidence of renal impairment, four had modest elevations of plasma urea and creatinine concentrations and six had acute reversible renal failure of whom three required peritoneal dialysis. Only one patient was hypovolaemic and in the remainder there was evidence that intravasular coagulation was responsible for the renal failure. It is suggested that bacteraemia was the initiating factor. The therapeutic implications of these findings are discussed.