Kidney Cysts

Kidney cysts are small, fluid-filled or solid pouches that form on or in your kidneys. Most people who have them don’t even know they do. You might need treatment if your cyst is complex, becomes infected or presses on other organs.


The human body showing the location of the kidney, with the kidney having three fluid-filled cysts on it.
A kidney cyst is a fluid-filled sac on or in your kidney. They can be small or large and you can have more than one. Most are harmless and not cancer.

What are kidney cysts?

Kidney cysts (renal cysts) are usually small, round sacs that have a thin wall and contain a watery fluid. As you get older, cysts can form on the surface of your kidneys or in structures inside your kidneys called nephrons.

Kidneys are the filtration system for your body. The nephrons are made up of a filter and a tube. As blood flows through your kidneys, the nephrons remove extra water and waste products, which leave your body as urine (pee). 

Kidney cysts can range in size, although most tend to be less than 2 inches wide. They can also grow over time or stay about the same size. Some people may have several cysts, while others have just one. You can have one or more cysts in one or both kidneys.

Kidney cysts typically don’t affect how well your kidneys work, and they’re usually not a cause for concern. In rare cases, a very large cyst can cause pain. Your healthcare provider may just want to monitor it and make note of it in your health history. In some cases, a kidney cyst is suspicious, and your provider may recommend additional tests or remove it.

Types of kidney cysts

There are generally two types of kidney cysts: simple and complex. Most kidney cysts are simple cysts. Healthcare providers use the Bosniak system to classify kidney cysts into five levels (named after the physician who developed the system).

Simple kidney cysts

Simple kidney cysts are almost always noncancerous (benign) and harmless. They typically don’t cause symptoms unless they become very large. You may not even know you have one. Simple cysts are fluid-filled and round, with thin walls. These are category I on the classification scale and don’t require any follow-up or treatment.

Complex kidney cysts

Complex kidney cysts have a chance of being or becoming cancerous. Your healthcare provider will monitor, treat or remove a complex cyst. They look different from a simple cyst. Complex kidney cysts may be solid (not filled with fluid), irregularly shaped or have a thick outer wall. Complex cysts are far less common than simple cysts.

Your provider will classify a complex cyst as II, II-F, III or IV. A level II cyst doesn’t require follow-up care, but a level II-F does (the F stands for follow-up). The risk of cancer for a II-F cyst is approximately 5%. A category III complex cyst has about a 50% to 80% chance of being cancerous, so your healthcare provider will remove it. A category IV cyst has about a 90% chance of being cancerous, so this type also requires removal.

Should I worry about a kidney cyst?

Simple kidney cysts are almost always harmless. They’re called simple because there’s little chance they’ll develop into something more serious. Complex cysts can sometimes be a sign of kidney cancer. Your healthcare provider will want to monitor cysts for changes that could be cancerous or remove the cyst.

How common are kidney cysts?

Simple kidney cysts are most common in people over 50. Up to half of people older than 50 will have at least one kidney cyst. People assigned male at birth (AMAB) are more likely to have kidney cysts than people assigned female at birth (AFAB). 


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Symptoms and Causes

What symptoms do kidney cysts cause?

Simple kidney cysts usually don’t cause any symptoms. In fact, most people who have them don’t know they have them. The cysts become a problem if they rupture (break open) and start to bleed, become infected, or grow so large that they push against other tissues and organs within your abdomen.

When simple kidney cysts do cause symptoms, they might include:

Depending on where the cyst is located, it can affect how your kidney works. It can also lead to a type of high blood pressure if the cyst prevents the kidney from filtering extra fluid from your blood.

What causes kidney cysts?

Kidney cysts occur when the tube of a nephron begins to swell and fill with fluid. Researchers don’t know what causes this, but they do know that simple cysts aren’t inherited (they don’t happen because of conditions you get from your biological parents). They believe an injury or microscopic blockages in the tubules may lead to the development of simple kidney cysts.

What are the risk factors for simple kidney cysts?

Healthcare providers aren’t entirely sure what makes people more likely to get kidney cysts, but they know you’re more likely to have them if you’re older than 50.

Some medical conditions can cause kidney cysts. These include:


What are the complications of simple kidney cysts?

Most kidney cysts don’t cause complications or long-term problems because they’re simple cysts. If your healthcare provider determines a cyst is complex, they may watch it for changes or remove it.

Kidney cysts can cause complications like:

  • Infection: The cyst becomes infected and causes pain, fever or other symptoms.
  • Blockage of urine: The cyst becomes large enough to block urine flow. This can cause kidney damage and infections.
  • Burst cyst: The cyst breaks open and causes pain, blood in your pee and other symptoms.
  • Bleeding Cyst: Bleeding occurs inside the cyst, which can break the cyst open and cause bleeding around your kidney.

Diagnosis and Tests

How are simple kidney cysts diagnosed?

Healthcare providers often find a simple kidney cyst by accident while performing imaging tests for another condition. If they notice a cyst, they may recommend other tests to see if the cyst is simple or complex.

  • Ultrasound: High-frequency soundwaves and echoes create images of your kidneys.
  • Computed tomography (CT): X-rays and computer processing produce 3D images of your kidneys.
  • Magnetic resonance imaging (MRI)An incredibly powerful magnet, radio waves and computer processing create images of your kidneys. An MRI can help your provider tell the difference between cysts filled with fluid and solid masses. 
  • Kidney function tests: Blood and urine tests can tell your provider how well your kidneys are working and if the cyst is affecting their function.

Your healthcare provider may determine a kidney cyst needs monitoring. If this is the case, they’ll likely repeat imaging tests every six months to two years. If the cyst causes symptoms between follow-up appointments, you should call your healthcare provider.


Management and Treatment

How is a kidney cyst treated?

In most cases, your provider won’t need to treat a simple kidney cyst. But, if a cyst is pressing on another organ or is affecting the way your kidney works, cyst removal might be necessary. If your provider believes the cyst is cancerous or could lead to cancer, they may also decide to remove it.

There are two procedures that healthcare providers use most often to treat kidney cysts:

  • Aspiration and sclerotherapy: Your provider inserts a long needle under your skin to puncture the cyst and drain the fluid. Sometimes, they’ll also inject a special solution into the cyst so it’s less likely to fill up again.
  • Surgery: Surgery to remove a cyst is usually laparoscopic. Your healthcare provider inserts thin instruments through small incisions in your abdomen. During surgery, your provider drains the cyst and then cuts or burns away the outer tissue of the cyst.


Can simple kidney cysts be prevented?

You can’t prevent a simple kidney cyst. You can only reduce your risk by:

Talk to your healthcare provider about ways you can best care for your kidneys.

Does a simple kidney cyst need to be watched over time?

It’s very important that a healthcare provider evaluate the type and location of a kidney cyst. There are often characteristics — such as cyst wall thickness, fluid density and irregular cyst wall shape — that may indicate the cyst is more likely to be, or could become, cancerous.

Generally, a small, simple cyst doesn’t need monitoring. But, your healthcare provider is the best person to determine if and how often you should return for a follow-up.

Outlook / Prognosis

What is the outlook for someone with kidney cysts?

Since simple kidney cysts are almost always harmless, the outlook is excellent. Treating a cyst due to infection, rupture or blockage is very effective and most people make a full recovery.

If you have a complex kidney cyst, your healthcare provider will either remove it or watch it closely for changes. Removing a complex cyst before it becomes cancerous is usually very effective with few complications.

Living With

When should I call my healthcare provider about kidney cysts?

You should call your healthcare provider if you experience any of the symptoms of a kidney cyst, such as:

  • Pain in your side, stomach or low back.
  • Blood in your pee.
  • Fever.
  • Changes in urination habits like peeing more or less often.

What questions should I ask my provider?

It’s natural to have questions about a diagnosis. Some questions you may want to ask include:

  • Will the cyst get larger?
  • What type of kidney cyst do I have?
  • Are my kidneys still working well?
  • What treatment do you recommend?
  • What are the pros and cons of the treatment options?
  • What symptoms could indicate a problem?
  • Do you recommend any lifestyle changes or adjustments to what I eat?

A note from Cleveland Clinic

Hearing you have a cyst on your kidney may sound alarming. But rest assured, kidney cysts are common and usually not a cause for concern. Your healthcare provider may recommend more tests to get a better look at the cyst to determine if treatment is necessary. Talk to your provider about what type of cyst you have and what it means for your health. Don’t be afraid to ask questions. In most cases, your provider will monitor the cyst over time and ask you to watch for signs of a problem like pain, fever or blood in your pee.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 01/24/2024.

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