A lesbian couple registered what officials called Mexico's first gay civil union on Wednesday in the northern city of Saltillo.
The couple, Karina Almaguer and Karla Lopez, traveled to Saltillo from their home state of Tamaulipas to register as a "civil solidarity union" under a newly passed law that made Coahuila the first of Mexico's 31 states to grant recognition to such unions.
Television footage showed the couple smiling broadly and shaking hands with officials after the simple ceremony at a registrar's office.
Coahuila State Assemblywoman Julieta Lopez Fuentes, who served as an official witness, said the law passed earlier this month allows people from other states to register such unions in Coahuila.
"The object of this law is that unions of people of the same sex be legally regulated and recognized, so that they can have some security in their future," she said.
Lopez Fuentes said it was the first gay civil union in Mexico.
In November, Mexico City — which as a semi-independent capital zone has some of the same powers as states — passed a similar measure, the first in the nation's history, but that law will not go into effect until mid-March.
Such laws, which provide gay couples with numerous social benefits similar to those of married couples, have been sharply criticized by the Roman Catholic Church and the conservative National Action Party of President Felipe Calderon.
While homosexuality is still taboo in many rural parts of Latin America, the region's urban areas are becoming more socially liberal.
Mexico City and Coahuila join the Argentine capital of Buenos Aires and the southern Brazilian state of Rio Grande do Sul in legalizing same-sex civil unions.
At the national level, lawmakers in Costa Rica and Colombia have debated, but not passed, similar measures.