The renal pelvis and ureter are conduits composed of interlacing bundles of spirally oriented smooth muscle, lined by urothelium. Their function depends upon the presence of intrinsically normal musculature and proper spatial orientation relative to the bladder. Surgical correction of malformations may involve excision of an intrinsically defective segment of the collecting system (as in ureteral diverticulum, congenital ureteropelvic junction obstruction, ureterocele, and primary megaureter), or the reconstitution of proper anatomy (as in correction of ureteral reflux, ureteral ectopia, or paraureteral diverticulum). The status of the musculature of an excised segment of the drainage system is of prime importance; the overlying mucosa is generally normal.