Chronic non-obstructive pyelonephritis has been followed for periods ranging from 18 to 40 years (mean 25), by using series of urographies and clinical examinations. The patients studied were fifteen adults, and eight children who were between the ages of three months and eleven years at their initial examinations. Among the adults, progressive scarring was found in 3 patients with renal calculi, the others remaining unchanged during the follow-up period. Among the children, progressive scarring was found in all affected kidneys, the scarring progressing during early childhood and adolescence, and then remaining unchanged during adult life. This retrospective study indicates that calyceal clubbing and parenchyma scarring occur during childhood and seldom progress without the intrusion of superimposing factors, such as renal stone formation.