A 36-month-old boy had acute gallbladder hydrops in association with mucocutaneous lymph node syndrome. A review of 46 other cases of this association has shown that patients having MLNS with gallbladder hydrops are older than those without gallbladder hydrops. The diagnosis is suggested by abdominal symptoms and abnormal results of liver function tests. The diagnosis is confirmed by ultrasonography, which shows the gallbladder to be twice the normal size. Cardiac complications may be increased. Treatment is largely supportive, but cholecystostomy is the procedure of choice in cases requiring operative intervention.