Brazil's 2010 census found 60,000 gay and lesbian couples, the government's Institute of Geography and Statistics said April 29.
Census takers asked respondents if they considered themselves a same-sex couple.
"We expected the figure to be lower than this," said Toni Reis, president of the Brazilian Lesbian, Gay, Bisexual and Trans Association. "In a heteronormative society many gay and lesbian people prefer not to reveal this sort of information for fear of discrimination."
Still, given Brazil's population of 190.7 million, Reis called the 60,000 figure "just the tip of the iceberg."
"Without a doubt, the number will be much higher in the next census in 10 years' time, as LGBT people become more open," he said.
The LGBT association ran a campaign to encourage same-sex couples to declare their relationship.
For the 2020 census, the organization plans to encourage the government to also ask about sexual orientation, "so that there will finally be official statistics estimating the size of Brazil's LGBT population and serving to orient public policies."