It is seldom realized that at least 90 per cent of major urologic problems are related to urinary tract obstruction, dysfunction, and infection. The importance of this is reflected in the vigorous campaign, waged by urologists for years, to salvage functionally impaired renal tissue. Today, “renal salvage” is becoming increasingly important as the incidence of trauma mounts. To save even a third of a kidney may be to save the tissue which preserves life in a future accident in which the opposite kidney is destroyed either temporarily or permanently. The most common site for supravesical congenital obstruction of the urinary tract is the ureteropelvic junction. Interest in determining the cause of such obstruction was stimulated in the course of an effort to establish a consistently successful corrective surgical procedure. This study will present a heretofore unrecognized cause of obstruction, with a description of an operation that has been unusually successful in re-establishing a morphologically and ph...