The Infrequent Voider Syndrome or Lazy Bladder Syndrome in children is characterized by a large capacity bladder, frequently associated with a significant volume of residual urine. Usually these patients arrive at medical examination with a history of recurrent urinary infections but without anomalies in the upper urinary tract. We report about a young girl affected by one-sided 20 degree vesico-ureteral reflux due to Lazy Bladder Syndrome that had never been diagnosed before. This patient has been submitted to a prompt bladder training and seems presently to have at last gained a physiological micturition after 9 months of follow-up,without actual evidence of vesico-ureteral reflux. Therefore we must stress that it is prominently important considering every notice about infrequent micturition in a paediatric case history or a large capacity bladder, noticed by chance too. These reports may be fundamental for early diagnosis of Lazy Bladder Syndrome.