In children more than one year old the growth rate of the renal parenchyma is delayed if the kidney has a large reflux-ureter and is exposed to urinary tract infection. The growth rate of the parenchyma is normal, if the kidney has a large reflux-ureter but no infection. However, since moderate reduction of the renal parenchyma is often observed in patients with large reflux-ureter but without a history of urinary tract infection, it is concluded that a large reflux may cause back pressure injury on the kidney during infancy but, in children more than one year old, will cause renal growth retardation and renal scarring only be predisposing to pyelonephritis.