Torsion of the gallbladder in a child is rare and only 23 cases in children have been reported in Japan. A preoperative diagnosis is very difficult and only four cases have been diagnosed, preoperatively, to date. In the case reported here the suspected preoperative diagnosis was an acute cholecystitis. During the operation, the gallbladder was found to be enlarged to twice the normal size and twisted 540 degrees in a clockwise direction around the cystic duct. A cholecystectomy with abdominal drainage was successfully performed; and the patient was discharged in good condition, 13 days after the operation. It was concluded that one of the most important features for the preoperative diagnosis of torsion of the gallbladder is a dislocation on ultrasonography.