A three-judge panel unanimously held that birth mothers have no constitutional right to have the records kept confidential. The court also lifted an injunction barring the state Health Division from releasing the records.
The measure was solidly passed by Oregonians in November 1998 but it never has taken effect. A trial judge upheld the law, but the appeals court had continued a stay preventing release of records.
The law says adoptees 21 or older can obtain their original birth certificates, which often contain birth parents' names.
Foes argue that the law unconstitutionally breaches rights of privacy and contract; the court rejected both contentions.
The decision could be appealed to the Oregon Supreme Court, which would decide whether to review the lower court decision.
A total of 1,468 Oregonians had applied to obtain their birth certificates as of Wednesday, the health agency said.
The chief sponsor of the law, Helen Hill, said the ruling will give adoptees like her the same rights as other people to know the identity of their biological parents.
"This is wonderful news for all of the people out there who have had one wall after another put in front of them all their lives," she said.
But a group that opposes Oregon's law, the National Council for Adoption, said the ruling opens the door to birth mothers being harassed by children they gave up for adoption with the understanding they would never be contacted.
"The state of Oregon is saying to all of the people who were promised privacy in the past, 'We were lying to you,' " said Bill Pierce, spokesman for the Washington, D.C.-based group.
Deputy Attorney General David Schuman had argued to the court that the "right to anonymous adoption was invented in 1957," referring to the Legislature's passage of a law that year sealing what had been open records.
The appeals court said the change in the confidentiality law didn't impair any contract rights agreements under either the state or federal constitutions.
The court also said birth mothers had no constitutional guarantee of privacy.
"At no time in Oregon's history have the adoption laws required the consent of, or even notice to, a birth mother on the opening of adoption records or sealed birth certificates," the appeals court said in an opinion written by Judge Paul De Muniz.
He said adoption "is not a fundamental right," so there's no basic right to have a child adopted with a pledge to keep the mother's identity secret.
The law has been watched by adoption advocates nationally. The Tennessee Supreme Court in September upheld a 1996 law giving adoptees access to their records. Just three other states -- Alaska, Kansas and Delaware -- have opened adopton records.