Acute urinary retention in children is rare. There are a variety of causes about the disease. We report a case of a 7-year-old girl with acute urinary retention and hematuria. Pelvic sonogram revealed an isoechoic mass in the urinary bladder that appeared as a lobulated filling defect over the bladder neck on intravenous urography and computed tomography studies. The surgical specimen from cystoscopic examination showed reactive changes on pathologic analysis. Cytomegalovirus was isolated from urine culture. The girl recovered after supportive treatment.