Urachal cyst abscess is atypical to occur in childhood. A 4-year-old girl with urachal cyst abscess who suffered from low abdominal pain and fever is presented. Under the impression of acute appendicitis, appendectomy and exploratory laparotomy were performed and a urachal cyst abscess was found and drained. Subsequent voiding cystourethrogram (VCUG) revealed bilateral grade II vesicoureteral reflux. Regular followed-up examinations revealed the patient was in good condition. The diagnosis and treatment in cases of infected urachal cyst were discussed, along with a review of previous literature.(Tzu-Chi Med J 1994; 6: 287-290)