SALT LAKE CITY -- The Utah Supreme Court overturned an unusual custody case Friday, saying a couple who have raised a 2-year-old boy for much of his life must return him to his biological parents.

The Supreme Court unanimously said a 3rd District Court judge applied the wrong law when he allowed Toni and Matt Worthington to have custody and deny visitation to Rachel Sullivan of Salt Lake City.

She was paid to become a surrogate mother and gave birth in July 2004. The father, Arturo Nuosci, of Las Vegas is serving a federal prison sentence for fraud.

"While the Worthingtons may have been proper temporary custodians ... the permanent award of custody of P.N. to legal strangers was impermissible," the court said.

The Worthingtons wanted to adopt the boy. Judge Bruce Lubeck didn't allow it but said it was in the child's best interest to stay with them. He also said they could keep the boy away from his biological parents.

The Supreme Court said that was wrong without "some specific finding of harm to the child."

Nuosci, a Canadian citizen living in Las Vegas, met Sullivan through a Web site and paid her $23,000 to have his child.

After the boy's birth, Nuosci was arrested for making a false application for a U.S. passport. Sullivan was contacted by Las Vegas authorities and brought the boy to Utah.

She, in turn, decided to place the baby with the Worthingtons -- but later changed her mind.

The case now returns to 3rd District Court to decide the boy's future like other custody disputes between biological parents.

The Supreme Court said it hopes Sullivan and Nuosci "will put aside their individual interests and focus instead on the needs of their small child, who has presumably enjoyed considerable affection, care and stability with the Worthingtons."

The justices encouraged the biological parents to "pursue a custody agreement in a cooperative manner and to include the Worthingtons in this process."