The time of disappearance of neonatal hydronephrosis is not specifically defined. In fewer cases, it tends to disappear within 6 months after birth. For those with large amount of fluid and abnormal renal function, it usually does not disappear on its own. 1. For those with less fluid accumulation and no urinary tract abnormality, this kind of hydronephrosis has a tendency to heal by itself. Regular ultrasound review is recommended, and most of them disappear within 6 months after birth. 2. Large amount of hydronephrosis with abnormal renal function: common causes include obstruction of pyeloureteral junction, vesicoureteral reflux, etc. This kind of hydronephrosis usually won’t go away by itself, so it is necessary to consult a doctor in time to find out the cause of the disease, and to formulate a treatment plan according to the situation under the guidance of the doctor. Newborns with hydronephrosis should actively seek medical attention to avoid aggravation of the condition.