Patient: Description of the condition (onset time, main symptoms, hospital visited, etc.): Now 19 months at birth there is left hydronephrosis, 1.3cm, gradually observed, May 2010 examination for 1.96cm, December 28 examination for the left hydronephrosis 2.3cm now, 80 * 39, the right 65 * 30 ureter without dilatation, the doctor let do imaging. Since birth, the child has not had any phenomenon. 1. What is the critical value of hydronephrosis and how much surgery is necessary to correct it? 2. If it is only stenosis, what can be reached if after surgery? Wang Xiang, Department of Urology, Pediatric Hospital of Fudan University