The renal growth in children with primary reflux, congenital hydronephrosis, non-refluxing megaloureter, neurogenic bladder, renovascular hypertension, solitary kidney and glomerulonephritis was investigated.<br>Renal ratio (renal length/length of L2 plus its disc), Parenchymal ratio (renal Parenchymal section area/renal section area) and Parenchym-Vertebral ratio (renal Parenchymal section area/the distance from the top of L1 to the bottom of L4 vertebral bodies×width of L2) in children with these diseases were compared with those in normal children.<br>1) Primary reflux: Renal ratio and Parenchymal ratio were useful to make prognosis and to follow up the primary reflux.<br>In 64% of grade 3 reflux, Parenchymal ratio of initial IVP was below -2 S. D. Before the 5 years of age the Parenchymal ratio was below -2 S. D. in only 17% while after the 6 years of age it was below -2 S. D. in 83% of the patients.<br>Disturbance of renal growth seems to appear after the 5 years of age, thus indicating antireflux surgery to be done before then in grade 3 reflux.<br>In grade 1 and 2 reflux, there is no indication for an immediate operation since there remains a possibility of spontaneous cessation of reflus providing Renal ratio and Parenchymal ratio were in the normal range.<br>2) Congenital hydronephrosis: Prenchymal ratio was the most useful index to determine the result of plastic surgery. In the follow up of renal growth after the operation, Parenchym-Vertebral ratio and Renal ratio were useful when compared with normal growth chart.<br>3) Non-refluxing megaloureter: By serial determination of Parenchymal ratio after the operation, we can perceive the improvement of the kidny, and if reflux occurred in the operated unit, we can predict it fairly accurately.<br>4) Congenital neurogenic bladder: The parenchyma) ratio and Renal ratio were under -2 S. D. in the initial IVP only in the refluxing kidney. The Renal ratio and Parenchymal ratio were useful in determining the choise of treatment for the neurogenic bladder.<br>5) In the children with suspected glomerulonephritis: Renal ratio and Parenchymal ratio were all in the normal range.<br>6) Congenital or acquired solitary kidney: In all solitary kidneys, Parenchymal ratio was normal. Renal ratio and Parenchym-Vertebral ratio were useful to estimate the rate of hypertrophy. Hypertrophy of residual kidney after unilateral nephrectomy was seen already in a month postoperatively and continued for another six months.<br>In two cases of Wilms tumor who demonstrated severe side effect from chemotherapy, hypertrophy was less significant than in another 3 cases without adverse reaction to it.