Slovenians were on Sunday voting in a referendum on whether to allow the largely-Catholic EU member state to become Europe's first ex-communist country to allow same-sex marriage.
Polling stations opened promptly at 7:00am (0600 GMT), although hardly anyone could be seen coming to vote in the first hour, an AFP correspondent in the southwestern port city of Koper said.
More than 1.7 million people are registered to cast their ballots on the issue which has stoked heated debate in this former Yugoslav republic.
In March, Slovenia's parliament approved legislation redefining marriage as a "union of two" instead of being a "union of a man and a woman", granting homosexual couples the same rights as their heterosexual counterparts, including the right to adopt children.
But opponents immediately launched a campaign to reverse the changes, meaning the legislation never came into force and no same-sex couples were able to tie the knot.
A group called "Children Are At Stake" managed to gather the 40,000 signatures necessary to force a referendum on the matter.
"I voted yes. Love is love, regardless of everything," said a 24-year-old woman called Ida.
Another voter said he was also in favour of the changes, but argued that putting the matter to a referendum was a waste of public money.
"It should be experts or the government deciding about this. They should not leave it to us," said Vojko, a pensioner.
"This is throwing money away. Of course I'm for it, but if it turns out to be a 'no', the world will laugh at us."
But the issue has divided this country with a population of around two million. On the wall of a church centre near the polling, someone had scrawled a question.
"Would you take a homosexual donor's blood to save your child?" it read.
Another pensioner said that while gay couples should be given equality as far as marriage was concerned, that should not include the right to adopt children.
"They are people like us, they should be given all rights, but not (the right to adopt) children," said a 76-year-old woman called Ema.
"It has to end with a 'no'."
Outside of Slovenia, same-sex marriage has already been legalised in 18 countries, including 13 in Europe. Ireland last May became the first country to approve gay marriage through a referendum.
Ahead of the vote in Slovenia, debate has been heated, and even Pope Francis has waded in, urging Slovenians to stand up for traditional family values.
Speaking to a group of pilgrims, he said he encouraged "everyone, especially those with public responsibility, to support the family, a structural reference point for the life of society."
A final poll released by state television on Friday gave the "No" vote 55.5 percent support, with a projected turnout of 46 percent. But other polls predicted a closer outcome.
In order for the result to be valid, the winning side must include at least 20 percent of eligible voters. Other surveys have indicated a tighter result, however.
If the "No" vote prevails, then the civil code will be changed back, although existing legislation, which allows registered civil partnerships but not the adoption of children, will remain in force.
This is not the first such referendum on the subject, with Slovenian voters rejecting gay marriage in an earlier plebiscite in 2012, although turnout was low.
Polls close at 9:00 pm (2000 GMT), with preliminary results expected shortly afterwards.
Slovenia has long been ahead of its peers, joining the EU back in 2004 -- nine years before neighbour Croatia -- and the eurozone in 2007 as its first ex-communist member, but its society retains a strong traditionalist streak.
President Borut Pahor and Prime Minister Miro Cerar's ruling Modern Centre Party (SMC) support the "Yes" camp, saying gay marriage would eliminate discrimination and grant equal rights to all citizens in the two-million-strong country.
"At this referendum we're deciding what kind of Slovenia we want to live in," Nika Kovac, a coordinator from the "Cas je Za" (It's time For a Yes) campaign group, told AFP.
"We'll decide whether we want to join the developed world."
Janez Jansa, the former centre-right prime minister from the opposition Slovenian Democratic Party (SDS), strongly disagreed.
"Erasing the gender from the marriage (definition) gives ground to human rights' violations against our most precious -- our children," Jansa said.