Acute acalculous cholecystitis is rare in non critically ill or postoperative patients. We report a case of acute acalculous cholecystitis with secondary bile infection with Clostridium perfringens. Ultrasound and tomodensitometry revealed diffuse aerobilia. The germ in this case report is atypical and contrasts with the very discrete clinical findings. Aerobilia, secondary to the development of bacteria in the biliary tract falsely suggested a bilio-digestive fistula. Treatment included a simple cholecystectomy associated with 7 days of antibiotherapy.