The French constitutional court has upheld a ban on gay marriage, which was challenged by a lesbian couple with four children.
The court ruled that the ban, challenged by Corinne Cestino and Sophie Hasslauer, was in keeping with the constitution.
Activists had hoped France would join states like Spain and Belgium in legalising same-sex marriage.
An opinion poll suggests most French people are in favour.
The TNS Sofres survey of 950 people suggests that 58% of French people approve while 35% oppose gay marriage.
Fifteen years together
The court, or Constitutional Council as it is formally known, reached its decision through a panel of eight judges, six men and two women.
While many European states recognise homosexual civil unions, only Spain, the Netherlands, Belgium, Portugal, Sweden, Norway and Iceland legally acknowledge same-sex marriage.
Ms Cestino and Ms Hasslauer have lived together 15 years, are raising four children together, and already benefit from a French law recognising their partnership, but they cannot marry.
"It is not so much about getting married but about having the right to get married," Ms Cestino, a paediatrician, told the Associated Press news agency.
"So, that is what we are asking for: just to be able, like anyone else, to choose to get married or not."
At issue for the court were two articles in the civil code stipulating that marriage can only be between a man and a woman.
The couple's lawyer had been hoping that the court would force the conservative government to sponsor a bill on gay marriage to send to parliament.
After a Green Party mayor in the south-western town of Begles officiated over a wedding of two gay men in 2004, France's highest court annulled the marriage.
Under their civil union, the lesbian couple have tax benefits and other financial advantages, their lawyer Emmanuel Ludot explained.
But marriage, he added, confers "the responsibility to help each other in times of sickness or financial difficulty, inheritance rights and the joint custody of goods - and that's without talking about the benefit for children, who are what we call 'legitimised by marriage'".
BBC News
