Why coused my kidney to get biger then the othet?

Blood flow: A big kidney on one side with a small one on the other, the classic cause is an interruption to blood flow to one or the other kidney. A serious infection, or trauma could also cause this. Assuming that this finding is from an ultrasound, a vascular study is probably needed. Talk with your doctor.

Many possibilities: Kidney blockage, congenital or acquired will make affected kidney larger, it will result in hydronephrosis. Duplex or double kidneys r normally larger than usual single system kidneys. Some dysplastic kidneys (developed abnormally) are small ; opposite kidney grows more ; is lager, same as childhood pyleonephritis after damage ; scarring to 1 kidney only. A cystic kidney can also enlarge more.