A stroke occurs when blood flow to the brain is interrupted. When this happens, brain cells begin to die because they don’t get the oxygen and nutrients they need to function. Even though a stroke occurs in the brain, the whole body can be affected, causing paralysis, problems with thinking and speaking, emotional difficulties, and other disabilities. A stroke is sometimes referred to as a “brain attack.”

A stroke can occur in individuals of any age, gender, or racial background. In the United States, stroke is more common in African Americans. Risk of stroke increases with age and is higher among people with a family history of stroke.

Stroke is the third leading cause of death in the United States and the most common cause of disability among U.S. adults. More than 700,000 Americans have a stroke each year, and there are about 160,000 stroke-related deaths annually.

Types of Stroke

  • Ischemic stroke: This type of stroke comprises about 80 percent of strokes. Causes of an ischemic stroke include: thrombosis, a clot within a blood vessel of the brain or neck; embolism, movement of a clot from another part of the body, such as from the heart to the neck or brain; or stenosis, a severe narrowing of an artery in or leading to the brain.
  • Hemorrhagic stroke: This type of stroke occurs when a blood vessel in the brain breaks and bleeds into the brain. About 20 percent of strokes are hemorrhagic.


The onset of a stroke is a medical emergency. If you experience or witness someone experiencing one or more of the following symptoms, call 9-1-1 immediately.

  • Sudden numbness or weakness of face, arm, or leg—especially on one side of the body.
  • Sudden confusion or trouble speaking or understanding speech
  • Sudden trouble seeing in one or both eyes
  • Sudden trouble walking, dizziness, or loss of balance and coordination
  • Sudden severe headache with no known cause

Other warning signs of a stroke can include double vision, drowsiness, and nausea or vomiting.

How Do I Know if I’ve Had a Stroke?

By responding to the warning signs of a stroke described above and seeking immediate emergency care, doctors will determine whether you’ve had a stroke. To do so, they’ll inquire about your symptoms and your medical history and perform tests including brain imaging and blood tests. Learn more about diagnosis of a stroke below in “Diagnosis.”

Causes of Stroke

The most common cause of a stroke is a blockage of a blood vessel in the brain or neck. This blockage is called an ischemic stroke. A stroke can also be caused by bleeding into the brain; this type of stroke is called a hemorrhagic stroke.

Preventing Stroke—Reducing Risk

There are several risk factors for stroke that you can control. Your doctor can help you determine your level of risk and help you take measures to reduce risk. If any of the following conditions or behaviors applies to you, take steps to manage or change them.

  • High blood pressure: Treat high blood pressure by eating a balanced diet, maintaining a healthy weight, and exercising. High blood pressure can also be treated with medication.
  • Cigarette smoking: If you do smoke, quit. Medical assistance and support can help.
  • Heart disease: Your doctor will develop a plan to manage heart disease. Management may involve medication and aspirin therapy as well as healthy lifestyle choices, such as diet and exercise.
  • Diabetes: Keep diabetes under control with diet, exercise, and medical treatment.
  • Transient ischemic attacks (TIAs): TIAs are small strokes. They last only for a few minutes or hours, but it’s critical that they are treated. Treatment includes medication or surgery.


The faster a stroke is diagnosed the better, as diagnosis enables doctors to begin appropriate treatment as soon as possible.

A priority of diagnosis is to determine whether the stroke is an ischemic or hemorrhagic stroke. This distinction must be made because it will determine which kind of medication is used—the medicine given for an ischemic stroke can be life-threatening if the patient has had a hemorrhagic stroke. Imaging of the brain with a computed tomography (CT) scan can help the doctor identify the type of stroke.

General steps in diagnosing a stroke include questions about the nature of symptoms and when they began, a medical history that includes questions about risk factors for stroke, and a physical exam that includes a short neurological exam. In addition to CT scan, tests that may be used to confirm a stroke diagnosis include blood tests, an MRI, tests for heart problems (such as electrocardiogram, or ECG or EKG), and imaging tests of the brain and arteries in the neck.

Several other conditions can cause conditions similar to a stroke. A doctor may consider the following conditions before making a diagnosis of stroke:

  • Bleeding just outside the brain
  • Brain tumor
  • Abscess
  • Low blood sugar
  • High blood sugar