Duplex kidneys are an congenital anomaly of the kidneys and urinary tract. In duplex kidneys there is a double kidney on one or both sides of the body.

We have two kidneys, which each have a single tube (called a ureter) that connects to the bladder. This tube drains urine from the kidneys into the bladder.

Kidney cross-section

In some pregnancies, the kidneys and ureters do not develop normally. One such variation is known as a DUPLEX KIDNEY.

Duplex kidney(s) means having a double kidney on one or both sides of the body. If a child has a duplex kidney this means that the area that collects urine (the renal pelvis) has split into two.

A duplex kidney can also mean a child has two ureters (tubes that drain the urine from the kidney to the bladder) instead of one.

You may be told that your baby has a possible duplex kidney during your pregnancy ultrasound scan or after your baby’s birth. You may need to go back to the hospital for further scans during the pregnancy and after birth. You may also be told your child has a duplex kidney if he /she has had a kidney ultrasound scan for urine infection. 

About the urinary system and kidneys

The kidneys are part of the urinary system, which gets rid of things that the body no longer needs so that we can grow and stay healthy.

The kidneys are bean-shaped organs. They filter blood and remove extra water, salt and waste in urine (wee). Most of us have two kidneys, which are at the back on either side of our spine (backbone), near the bottom edge of our ribs.

Other parts of the urinary system are:

  • two ureters – long tubes that carry urine from the kidneys to the bladder
  • bladder – muscular bag that stores urine until we are ready to pass urine
  • urethra – tube that carries urine from the bladder out of the body.

About duplex kidneys

Duplex kidneys are one type of congenital renal anomaly:

  • congenital – the problem is present at birth
  • renal – to do with the kidneys
  • anomaly – different from normal.

How duplex kidneys happen

Duplex Kidney illustration Children's Hospital of Philadelphia
Image provided courtesy of Children's Hospital of Philadelphia. © The Children’s Hospital of Philadelphia. All rights reserved.

While a baby is growing in the uterus (womb), the ureters normally grow into the kidneys and become the part of the kidney (the renal pelvis) that collects urine. Urine is drained from the kidney into the renal pelvis, through the ureters and into the bladder.

In duplex kidneys there is a variation in how the renal pelvis and ureters have developed when the baby was in the womb and how they connect to the bladder. Two main variations occur.

If there are two completely separate tubes (ureters) draining from the kidney into the bladder this is known as complete duplication.

If there are initially two tubes (ureters) draining from the kidney that then join together to form one tube that connects to the bladder, this is known as a partial duplication. Partial duplication is more common than complete duplication.

How common are duplex kidneys?

Duplex kidneys are the most common congenital abnormality of the urinary tract. It is thought that around 1% of people have duplex kidneys. This can often be an incidental finding on a scan (in other words, found out by accident).

Most babies and children do not have any symptoms after birth, however, if duplex kidneys are associated with other abnormalities in the urinary tract, there is a risk of urinary tract infections (UTIs). Symptoms can include fever, vomiting, pain on passing urine, abdominal or back pain, needing to pass urine more frequently. Other problems could include:

Vesicoureteral reflux

Urine travels back up the tubes from the bladder to the kidneys (it goes in the opposite direction it should do normally). This may be associated with symptoms of a urinary infection, bloody or cloudy urine.

Ectopic ureters

The tubes draining urine from the kidney connect to the bladder in an abnormal place or not to the bladder at all, which may cause urinary dribbling (incontinence).


This is a swelling “ballooning” at the bottom of the ureter inside the bladder, where the ureter (tube) that drains the upper pole (part) of the kidney has ‘ballooned’ as it enters the bladder.


One of the ureters (usually the ureter or tube that drains the upper pole (part) of the kidney) may be blocked, causing a dilatation of the drainage system of that part of the kidney, as shown in the image below, where the ureter draining the upper part of the kidney is blocked.

Weigert Meyer rule illustration Dr Matt Skalski
Image courtesy of Dr Matt Skalski, Radiopaedia.org

More information

  • About the urinary system and kidneys

    If your child has a health condition that affects their kidneys or another part of the urinary system, you may wish to find out more.

  • Tests and diagnosis

    Find out more detail about some of the tests used to diagnose or investigate kidney conditions.

  • Ultrasound scan

    Uses sound waves to look at the inside of the body, such as the kidneys and other parts of the urinary system.