Sept. 5, 2006  -- Everyone wants to fall in love.

It's the stuff of movies, songs and dreams.

But what if you fall in love with your cousin?

For two cousins, romance bloomed when they met as adults after a 20-year absence.

"We ran into each other, at a family reunion," Christie Smith said. "And we just struck it off."

Smith said marrying her cousin, Mark, brought concerns.

"It was very scary, at first. I thought that it was something that was very wrong," she said.

Einstein Kissed His Cuz

Cousins who fall in love have a right to voice concerns. After all, marrying a cousin just isn't done, right?

At least that's what we're taught to believe. Only primitive people who live in isolated places marry cousins, and it's dangerous and leads to creating stupid children.

Or does it? A new study reveals the genetic risks associated with this type of pairing are not as great as once believed.

And consider this — Albert Einstein's parents were cousins, and he married his cousin, too.

FDR and Eleanor Roosevelt were second cousins, so were Prince Albert and Queen Victoria and former New York City Mayor Rudolph Giuliani was briefly married to a second cousin.

In America, marrying your cousin is legal in 25 states and every year about 200,000 cousins wed.

Worldwide, it's much more common. Twenty percent of all married couples are cousins. In some Middle Eastern countries, almost half of all marriages are to cousins.

Those Who Say 'I Do'

But in America, cousins who find love also find public resistance.

"The overbearing concept is that, you know, 'Cousins can't get married,'" said Brian Wagner, who has been married to his cousin, Caren, for 14 years.

His dad and his wife's mom are brother and sister.

"Some people see it as 'inbreeding,' or, you know, 'incest,' or something terrible like that," he said.

Caren said she didn't plan on their shared future, although her mom noticed they always liked each other.

"They played together. They fought over toys together. And they just had a happy good relationship as kids will," said Pat Bradfield. "They were real kissin' cousins."

They initially grew up in the same area, but then Brian's family moved away. Years later when Caren visited, their lives changed.

"When she showed up at the airport terminal and come off the plane, it's just like everything came rushing back again," Brian said.

"It developed beyond a 'friendship,' into a 'OK, do you want to get married this weekend or next?'" Caren said.

Her mom says the idea "floored" her a bit, but because she couldn't stop the marriage she was leery of voicing opposition in fear of losing contact with her daughter.

Instead, she offered some advice.

"In a marriage such as you're contemplating, you have to remember that you could divorce your husband but you can't divorce the whole family," Pat said.

They lost one friend whom, Caren said, they just didn't hear from anymore after they announced their union.

Legality of the Marriage

Twenty-four states forbid cousin marriages.

The United States is the only western country in the world where these laws still exist.

"A lot of these laws have been on the books forever, and they have just not gotten changed," Brian said.

The laws date back hundreds of years to the time when the Catholic Church campaigned against cousin marriages because in the Bible Leviticus says, "None of you shall approach to any that is near of kin."

Regardless, Caren and Brian had a church wedding in Virginia, one of 25 states where cousin marriage is legal.

"We talked to our minister. … And he knew and he didn't have an issue with marrying us," said Brian.

Biological Implications

One of the reasons cousin marriage is taboo, is the assumption they will have kids with birth defects.

But a new groundbreaking study funded by the National Society of Genetic Counselors revealed that some beliefs about cousin marriage were unfounded.

Robin Bennett, who headed the study, told ABC News that the risks of having a child with a cousin were about "2 [percent] to 3 percent" above the average population's risk for having a child with birth defects or mental retardation.

She says while there are risks, they're "not as bad" as people perceive.

Other risk factors are higher. For example, there's a 10 percent chance that a 41-year-old woman will give birth to kids with chromosomal defects.

If one parent has a genetic disease, like Huntington's, they have a 50 percent chance of passing it on.

Bennett gives parents the risks but will not tell them not to have kids.

She advocates that cousins who are romantically involved have genetic counseling before they get pregnant.

Brian and Caren went for counseling and were told the risk for birth defects was low, but their kids might have asthma, which runs in the family.

They now have two boys, ages 14 and 10, and both have asthma. But they don't think twice about their parents being cousins. They're also at the top of their classes in school.

The rest of the family has come around and say they couldn't be happier with how things have worked out.

Ultimately, Caren and Brian say it may have been their family connection that led them to fall in love.

"We could communicate," Brian said. "We had the same values, as far as raising children. … It's a match."

This story was originally broadcast on "20/20" Aug. 6, 2004.