Biden was transferred Tuesday evening to the Thomas Jefferson University Hospital in Philadelphia for observation and tests, following his morning check-in to a Delaware hospital.
He is in good spirits and talking with his family, according to a statement from his doctors.
For the Bidens, who have a family history of vascular problems, it was a real scare.
It's difficult to say whether family medical history played any part in Beau Biden's stroke and what the cause could have been, said ABC News' Dr. Richard Besser, but strokes are more common in young adults than people may think.
An estimated 10 to 15 percent of strokes -- most of them ischemic or due to blood clots, rather than hemorrhaging -- occur in people under 45.
In the elderly, strokes are normally caused by the hardening of arteries and plaque that goes to the brain. In young people, the reason is usually a defect in the heart or a tear in an artery that causes a clot, which can go to the brain and cause a stroke, Besser said on "Good Morning America."
Biden likely didn't have an aneurysm, like his father.
"If you have an aneurysm and it ruptures, causes bleeding, that can cause a stroke," Besser said. "But you wouldn't expect a rapid recovery like we're hearing about here," Besser said.
There are three key symptoms of a stroke -- facial drooping, lack of ability to lift arms and slurred speech. Besser said if people experience any one of the three, they should immediately go to the hospital. Similarly, severe headaches can also be dangerous.
If you have the "worst headache of your life, be seen," Besser said. "Or if you have a headache that has any tingling or any neurological signs in your body, be seen right away."
Doctors say the next step is to conduct more diagnostic tests to determine what caused Biden's stroke, in order to prevent it from happening again.
Biden, who was elected as Delaware's attorney general in 2006, is physically fit. He recently served in Iraq for one year as a captain with the Delaware Army National Guard.
But doctors say fitness and youth are no guarantee against strokes, the third leading cause of death in the United States, behind heart disease and cancer.
Young men over the age of 30 are more prone to strokes than women, who are more vulnerable under 30. African Americans are also more likely to suffer a stroke at a young age.
Stroke kills about 137,000 Americans a year, according to the Centers for Disease Control and Prevention. It is also the leading cause of disability.
Danger of Strokes
More than 700,000 Americans, some of them young and seemingly healthy, have a stroke each year; women have about 55,000 more than men.
Because less is known about this disease among young people, the American Academy of Neurology has just received a grant to study stroke in that population, according to Dr. Aneesh Singhal, associate professor of neurology at Harvard Medical School, who practices at Massachusetts General Hospital in Boston.
"The risk is still very low, but young men and women need to be aware," said Singhal. "Stroke is the leading cause of disability worldwide. It can happen in the young, and one of the real problems is they don't recognize the symptoms and it is often overlooked in the emergency department when they visit."
Just last year, a Wayne State University study revealed that young adults arriving in hospital emergency rooms after a stroke are often misdiagnosed.
Researchers found eight of 57 stroke patients were incorrectly diagnosed with conditions including vertigo, migraine, alcohol intoxication, seizure, an inner ear disorder or other conditions.
Studies show that about 795,000 people suffer a new or recurrent stroke each year. About 610,000 of these are first attacks and 185,000 are recurrent attacks. Women account for 60 percent of stroke deaths.
Consequences of a Stroke
A stroke, sometimes called a brain attack, occurs when a clot blocks the blood supply to the brain (ischemic stroke) or when a blood vessel in the brain bursts (hemorrhagic stroke).
It can cause disabilities such as paralysis, speech and, especially among young people, emotional problems.
The first hours are critical in treatment. In the case of an ischemic stroke, the most common among the young, doctors can administer the clot-busting drug tissue plasminogen activator, or tPA, the only U.S. government-approved treatment for acute stroke. It must be given within three hours of the onset of symptoms to reduce permanent disability.
"Recovery rates in the young are much better than when you are older, but up to half of all patients still have symptoms and a third are unable to return to work," said Singhal. "The psychological impact, the social and emotional changes after stroke are much bigger in the younger population."
Risk factors for ischemic stroke in young adults include a personal and familial history of migraines, smoking and, in women, oral contraceptives.
Women who have all three risk factors have a 16 times greater chance of having a stroke, according to Singhal. There have been some associations between stroke and preeclampsia in pregnancy.
In younger people, stroke can be related to cardiac and blood vessel abnormalities, substance abuse, contraception or even lupus. Drugs, such as cocaine, ecstasy, amphetamines and other drugs that cause arterial narrowing can precipitate stroke.
Arterial dissection -- when arteries tear due to a minor trauma -- can also be a cause.
"If you stretch your neck in an awkward position or have a contact injury in racquetball or tennis or fall and hit your head, a little tear in the artery can be a source of clot formation," he said.
Another common cause in both males and females is a congenital hole in the heart.
For the Bidens, the hospital vigil is a familiar scene. Biden's mother and infant sister died in a tragic car accident in 1972.
"One of my earliest memories was being in that hospital, my dad always at our side. We, my brother and I -- not the Senate, were all he cared about," Biden recalled at the 2008 convention in a speech that brought tears to Michelle Obama's eyes.
Six months ago, Biden was thought to be a shoo-in for the Senate seat his father held for 36 years. But he announced in January he would not run, telling ABC News in an interview, "I'm gonna, first things first, make sure I focus on my family."
The National Stroke Association recommends the F.A.S.T. test as a quick screening tool to identify strokes:
Face -- Ask the person to smile. Does one side of the face droop?
Arms -- Ask the person to raise both arms. Does one arm drift downward?
Speech -- - Ask the person to repeat a simple sentence. Are the words slurred? Can they repeat the sentence correctly?
Time -- If the person shows any of these symptoms, time Is important. Call 911 or Get to the hospital. Brain cells Are dying.
ABC News' Kristina Wong contributed to this report.