Hydronephrosis describes a urinary tract abnormality where hydrostatic dilatation of the renal pelvis and calyces exists and considered as a hallmark for obstruction to urine flow downstream. Detecting the pathologic hydronephrosis cases along with the cause using the least invasive techniques is a matter of interest since ages especially in pediatric community. In the Iraqi healthcare practice, many cases are referred for advanced urology imaging tests without clear rational. This study aims to evaluate the rational of referring hydronephrosis pediatric cases to renal scintigraphy studies by comparing the results with the ultrasonography using particular parameters. A cross-sectional observational study involved prospective measurement of a number of variables via two main radiology techniques; sonography and scintigraphy was carried on in Baghdad, Iraq. Classical US and dynamic renal MAG-3 were performed on the same day for each of 35 children aged between 1-5 years presumed or suspected to have obstructive type of hydronephrosis by earlier US work-up. Results revealed a clear statistical significance between normal differential renal function and the good quality of renal drainage of Mag-3 test with the undilated PCS category (p-value 0.028) when measured by our team using the sonography technique. Other results of the calyceal dimension (CD) and the parenchymal thickness (PT) have failed to obtain a statistical significant difference when compared with the categories of the three variables of MAG-3. This study supports the inference of assessing renal function based on sensitive parameters of evolutionary sonography. Each radiologist/nephrologist/urologist should evaluate the measurement of reliable parameters of sonography especially the anteroposterior diameter of the pelvicalyceal system (APD of PCS) at the hilum area and the parenchymal thickness (PT) in millimeters and set the pediatric patient for logical follow-up before recommending the dynamic scintigraphy tests.