An organisation that furthers gay rights through litigation has hailed a federal court decision on same-sex adoption as “a major victory for same-sex parents.”

A US District Court judge in Louisiana has ordered the state registrar to honour the New York adoption of a baby boy by a same-sex couple, saying her continued failure to do so violated the US Constitution.

Lambda Legal represented Oren Adar and Mickey Smith, a gay couple who adopted their Louisiana-born son in 2006 in a New York court, where a judge issued an adoption decree.

When Smith attempted get a new birth certificate for their child, in part so he could add his son to his health insurance, the office of State Registrar Darlene Smith told him that Louisiana does not recognise adoption by unmarried parents and so could not issue it.

Lambda Legal filed suit on behalf of Adar and Smith in October 2007, saying that the registrar was violating the Full Faith and Credit Clause of the US Constitution by refusing to recognise the New York adoption.

The Constitution says that judgements and orders issued by a court in one state are legally binding in other states as well.

The Louisiana attorney general disagreed, and advised the registrar that she did not have to honour an adoption from another state that would not have been granted under Louisiana law had the couple lived and adopted there.

On Tuesday, US District Judge Jay Zainey ruled against the registrar and issued a summary judgment ordering her to issue a new birth certificate identifying both Oren Adar and Mickey Smith as the boy’s parents.

“It’s been a long three years, but clearly we’re very happy,” said Adar, who now lives with Smith and their son in San Diego.

“As an adopted child myself, I understand the need to feel like you belong. I remember as a child wanting to see my own birth certificate and to see my parents listed because it gave me a sense of belonging, of identity and of dignity.

“I want our child to see Mickey’s name and my name as parents on his birth certificate.”