Renal duplication is a common congenital anomaly of the urinary tract. In complete duplication, the kidney is drained via two separate renal pelves and ureters. According to the Weigert-Meyer rule, the upper pole often inserts inferior and medial to the site of the normal ureteral insertion. It is often associated with a ureterocele. The upper pole ureter may insert into the urethra, uterus, vagina, ejaculatory duct, seminal vescicle, or vas deferens. The lower pole's ureter tends to insert in the urinary bladder at the normal location.

While patients with unobstructed duplications do not have clinical problems more frequently than those with non-duplicated collecting systems, those with complicated duplications may present with abdominal mass, hematuria, incontinence, and urinary tract infections.

Renal duplication is detected via ultrasound when the central renal complex is separated into two parts by a column of normal renal parenchyma, a column of Bertin. When the upper pole moiety is obstructed, its dilated collecting system and ureter can be seen. If associated with a ureterocele, a cystic mass can be seen within the urinary bladder. If large enough, the ureterocele can cross midline and cause bladder outlet or contralateral ureteral obstruction. While the lower pole's ureter inserts at a normal location, it often refluxes, perhaps leading to additional complications.