Four months after 16-year-old sweethearts Leanne Detmer and Dallas Mills started dating, she got pregnant.

Now Leanne's parents are suing the boy's mother, saying she knew the kids were having sex and failed to control her son. In what may be the first case of its kind in the country, the Detmers charge that their daughter, who had an abortion, suffered extensive psychological and physical damage.The idea of holding parents responsible for their children's consensual sexual behavior is novel, said Simon Heller, a lawyer with the Center for Reproductive Law and Policy in New York.

If the lawsuit proceeds, he said Tuesday, it could compel parents to watch over their children's sex lives more closely. "On the other hand, it is clear that in my view, teenagers do have some constitutional rights to engage in sexual activity," Heller said.

In the Lancaster County lawsuit filed last August, Doug and Sharon Detmer say they did not know the teens were having sex until their daughter told them she was pregnant in April 1997. They do not specify how the boy's mother, Dawn Bixler, supposedly knew about the sexual activity.

The Detmers are seeking $11,371 in medical expenses, including the cost of the abortion and costs associated with their daughter's depression, plus other, unspecified damages.

In a pretrial ruling, Judge Jeffre Cheuvront dropped the boy from the lawsuit, saying the sex was consensual. But he said questions about the mother's responsibility should be decided at trial.