SAN ANTONIO -- It came out of the blue.

Lynn Riley was feeling perfectly fine when she went to bed the night before, but early on the morning of Dec. 1 last year, she woke to find she couldn't move the right side of her body.

"I knew I had to get out of bed because I live with my mother and stepfather, and they were going out for the day, so I'd be alone," she recalls. "I fell out of bed, and somehow I managed to get to the bedroom door. I don't know how I did it, but I walked down the hall to the breakfast room. I told my mother I thought I was having a stroke, and then I just collapsed, slid down to the floor, and they called EMS."

Riley, 61, was rushed to the hospital, where an acute stroke team began running tests and treating her. She'd suffered a lacunar stroke, a type of ischemic stroke that occurs when a small artery deep inside the brain is blocked by a clot.

Brain cells in the area can be damaged or killed by a lack of oxygen. She was monitored very closely that day because it is not unusual for stroke patients to have additional strokes after the first one.

After a week in the hospital, she went through about a month of inpatient rehab, then another month of outpatient physical therapy. Occupational therapy continues.

As with heart attacks, many people believe strokes affect primarily men. But national statistics and the experiences of women such as Riley tell a different story.

The fact is stroke affects women in significant numbers and is gaining more attention from physicians and researchers, who are studying gender differences in symptoms that could improve treatment.

Overall, stroke is the country's third leading killer. About 700,000 Americans will have one this year, according to the American Stroke Association. But 55 percent of all strokes and 60 percent of stroke deaths occur in women. About 100,000 women die annually of stroke, 40,000 more than the number of men who die from it. The fact that risk goes up with age and that women live longer account for a large portion of that difference.

"It seems to fly in the face of conventional wisdom that says men are at greater risk than women, and it's true, they are. But as they (men and women) get older, the difference is less and less apparent," says physician David Sherman, chief of neurology at the University of Texas Health Science Center and one of five acute stroke team neurologists at University Hospital who are on pagers, 24/7, ready to respond to emergencies.

Strokes can affect younger women as well, including after childbirth when the blood is more likely to clot -- probably an evolutionary adaptation so new mothers don't bleed to death, Sherman says. And for women who have migraine headaches -- about 18 percent of women do -- and those who smoke and take oral contraceptives, there is more risk of stroke.

Neurologists also see a younger stroke population due to the high incidence of diabetes and hypertension, both of which affect the small vessels of the brain. Other risk factors include high cholesterol, family history, untreated heart disease, carotid artery disease, sickle cell anemia and tiny, sometimes imperceptible, undiagnosed strokes called TIAs, or transient ischemic attacks.

Family history can play a role as well, and the genetic component of stroke is a growing area of study. Riley never smoked and didn't have diabetes, high blood pressure or high cholesterol, but two uncles and an aunt died of stroke, and her father died of a heart attack.

A CT scan showed that at some point in the past, she had had two small strokes, but she was unaware of any symptoms.

"Male or female, if you knock out a blood vessel in the brain, you're going to have similar deficits," says Anne D. Leonard, a registered nurse on the acute stroke team.

Treatment depends on the type and location of the stroke. The crucial factor in treating ischemic strokes is speed. A clot- busting drug called tPAmust be given within three hours of the onset of stroke symptoms, and only if the patient's blood pressure is in acceptable range and a CT scan shows no bleeding. In Riley's case, doctors weren't sure when during the night or early morning her stroke hit.

With the classic symptoms of stroke, the arms, legs and face on one side of the body suddenly go numb and the person may not be able to walk or speak. But data gathered from stroke patients in Texas in one study showed that women more often experience nontraditional symptoms, such as sudden pain on one side of the body or loss of consciousness or disorientation.