CLEVELAND -- Gastric bypass surgery is helping obese patients live longer and healthier lives. But a new study says that this surgery can be a lot more dangerous than people realize.

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And the heaviest patients may face the most risks.

Sally Scoville found she could do less and less every day because she weighed more than 300 pounds.

"I wouldn't go to a movie theater because I was so uncomfortable in the chair," Scoville said.

She decided to have gastric bypass surgery and has lost 160 pounds.

Scoville is one of the success stories when it comes to this procedure. But what a lot of people don't know is that there can be very serious complications after the surgery.

"It was scary because they were talking about something being wrong with my heart and possibly needing open heart surgery," said Scoville.

Dr. Thomas Stellato, who conducted Scoville's gastric bypass at University Hospitals in Cleveland, is also a researcher of a study released this week at a meeting of the Radiological Society of North America.

Gastric bypass surgery involves stapling the upper stomach to create a small pouch that is then attached to the small intestine, reducing the capacity of the stomach.

"This should not be considered a cosmetic procedure," said Dr. Elmar Merkle, a radiologist at Duke University Medical Center in Durham, N.C., and lead researcher on the study.

The study, which included 335 gastric bypass surgery patients, identified 57 different complications from the proceudre, including lung clots, torn stitches, tears, leaks, pneumonia and infection. There were also two deaths reported within 30 days after the surgeries.

"It has complications. Some of the complications are because of the magnitude of the operation, some of the complications are the associated problems some of the patients have," said Stellato.

Stellato said that the more obese the patient is, the higher their risk -- but those are the patients who need the surgery the most.

Scoville does have a few minor health issues, but she also has the freedom to do so much more than she used to.

"I'd walk right down the hall right now and have it done all over again," said Scoville.

American Society for Bariatric Surgery estimates that the 63,000 procedures performed in 2002 will increase to 100,000 this year.

Americans who are at least 100 pounds overweight are eligible for gastrointestinal surgery, according to National Institutes of Health guidelines, but a patient who is less than 100 pounds overweight may also be considered if there is a life-threatening condition related to his or her obesity, such as type 2 diabetes or cardiopulmonary problems.

But not every obese person is eligible for surgery. You are required to show proof that you've tried other ways of losing weight, you can't gain weight before the surgery, and you have to refrain from smoking for three months.

"People need to be aware of the potential complications of this surgery. It basically should be the last option we can offer the morbidly obese, after other less invasive interventions such as diet and exercise have been tried," Merkle said.

Stellato said the surgery can be a lifesaver for the right patient, but he said a procudure like this must never be taken lightly, despite its recent popularity.