Mexico's supreme court has ruled that same-sex marriages in Mexico City must be recognised throughout the country.
The ruling does not mean other states have to allow gay weddings on their territory.
Two of the court's 11 judges voted against the measure, arguing that it would damage the harmony of the federal system.
Last week the supreme court ruled that the law allowing gay marriages in the capital was constitutional.
The court will now consider the legality of allowing adoption by gay couples.
Mexico City's local assembly passed the law in December, giving gay people full marital rights, including the right to adopt.
Hundreds of gay and lesbian couples have since been married.
However, the law drew strong opposition from the Catholic Church and conservative groups, including the governing PAN party, and federal prosecutors challenged it on constitutional grounds.
Mexico City was one of the first Latin American capitals to fully recognise same-sex marriages.
The BBC's Inma Gil in Mexico City says gay relationships are openly accepted in the capital.
But she says the difference in attitude in the rest of the country is huge.
It is not clear how the court's ruling that the validity of same-sex marriages must be respected will be interpreted in states where they are not allowed.
So far in Latin America, only Argentina has legalised gay marriages nationwide.
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