The first investigation is an Ultrasound of the abdomen. The kidney on the affected side will show a dilated pelvis, thickness of the parenchyma of that kidney will be remarkably thinned out. The ureter may not be seen, or, if seen will be normal. This will show that the obstruction is proximal to the ureter. However, dilated pelvis does not always mean obstruction, so a second investigation to confirm obstruction is required. A Radio Nuclear Scan DTPA is a must. This investigation gives a lot of information useful for knowing the individual function of the 2 kidneys, also after therapy, the Scan should show that the function of that kidney has improved. This will be a clear indication that the treatment has helped and the function has recovered. Thus, this investigation will show how less the function has come down, how severe is the obstruction and based on these the decision to operate or not is taken. Routine investigations for any major surgery are carried out before posting the child for surgery.