INTRODUCTION:Urachal cyst is an exceptionally rare disease in children caused by the incomplete obliteration of the urachal remnant. Urachal cysts seldom cause symptoms unless a secondary infection occurs. The symptoms of an infected urachal cyst are nonspecific and may be similar to acute appendicitis or other acute abdominal conditions. However, complications attributable to a delayed diagnosis can endanger the life of a patient. PATIENT CONCERNS:A 5-year-old boy presented with a 3-day history of severe intermittent lower abdominal pain. DIAGNOSIS:Infected urachal cyst. INTERVENTIONS:The patient was treated with surgical resection of the urachus, followed by intravenous antibiotics during the hospitalization. OUTCOMES:The patient was discharged without incident 7 days after the operation. With his follow-up in our out-patient department, he recovered well without any sequelae in the 6 months post-surgery. CONCLUSION:We suggested using the abdominal echo scan to differentiate the urachal cyst because of its high sensitivity and nonradioactive characteristic, and computed tomography is a typical diagnostic tool for urachal cysts. The mainstream management of an infected urachal cyst remains surgical excision. Complete excision of urachal cysts is relatively easy in a pediatric patient and the risk of subsequent infection is low; however, patients tend to have a low, although possible, risk of potential malignant transformation over their lifetimes.