A 7-year-old girl was diagnosed with viral enteritis and was admitted to our hospital. Sudden right upper quadrant tenderness appeared 2 days after admission. Ultrasonography revealed a large thick-walled cystic gallbladder and an inflammation-induced hyperechoic cystic duct. The long axis of the gallbladder was in a horizontal rather than a vertical alignment. Computed tomography demonstrated a markedly enlarged gallbladder with a slightly thickened wall and an enhanced twisted cystic pedicle. The diagnosis of gallbladder torsion led to laparoscopic detorsion and cholecystectomy. The gallbladder was gangrenous and was rotated counterclockwise with the attachment of the mesentery to the inferior surface of the liver. Although it occurs more rarely in children than in adults, torsion of the gallbladder must be considered in the differential diagnosis of an acute abdomen. Early diagnosis and immediate laparoscopic intervention can help to achieve an excellent patient outcome.