Hydronephrosis which is defined as dilation of the renal pelvis and /or calyces is one the most common renal abnormalities among children and because of screening Ultrasound during pregnancy ,it is diagnosed frequently antenatally. Range of abnormalities which could cause hydronephrosis include vesicoureteral reflux, ureteropelvic junction obstruction (UPJO), ureterovesical junction obstruction or megacystis megaureter and transient hydronephrosis which its etiology is not clearly determined so far. No unique grading system is available but two mostly used grading systems includes SFU (The Society for Fetal Urology) and the measurement of the anteroposterior diameter of the renal pelvis (APD) represent the two most common standardized systems. SFU is aqualitative assesment regarding the dilatation of pelvis and calyses and its grading is as following: grade 0 no dilatation, calyceal walls are opposed to each other grade 1 (mild) dilatation of the renal pelvis without dilatation of the calyces (can also occur in the extrarenal pelvis) no parenchymal atrophy grade 2 (mild) dilatation of the renal pelvis (mild) and calyces (pelvicalyceal pattern is retained) no parenchymal atrophy grade 3 (moderate) moderate dilatation of the renal pelvis and calyces blunting of fornices and flattening of papillae mild cortical thinning may be seen grade 4 (severe) gross dilatation of the renal pelvis and calyces, which appear ballooned loss of borders between the renal pelvis and calyces renal atrophy seen as cortical thinning The quantitative APD technique grading includes: normal: 0–4 mm, mild: 5–9 mm, moderate: 10–15 mm, and severe greater than 15 mm. The more the grading, the more possibility of obstruction or severe vesicoureteral reflux. In this panel discussion with presence of pediatric radiologist, pediatric urologists and nephrologist, we are going to discuss about the advantages and disadvantages of each methods and to evaluate in which circumstances we should use further imaging modalities such as VCUG, MRU or radioisotope scan and to evaluate which measurement system is mostly used by clinicians for decision making about follow up of patients or surgical intervention and the proper follow up timing also would be discussed.