Bosnian Serbs have voted overwhelmingly to keep 9 January as a national holiday in defiance of Bosnia’s highest court.
With more than 70% of votes counted in Sunday’s referendum, 99.8% supported the holiday, authorities said.
The court ruled the date discriminated against Muslim Bosniaks and Catholic Croats and should be changed.
Serbs declared the creation of their own state within Bosnia on 9 January 1992, fuelling an ethnic conflict in which about 100,000 people died.
Bosnia is still split along ethnic lines between the mainly-Serb entity and a Muslim-Croat federation.
The Constitutional Court, based in the Bosnian capital Sarajevo, banned the referendum.
About 1.2 million people were eligible to vote and authorities said turnout was more than 56%.
Bosnian Serb President Milorad Dodik said the referendum would go down in history as the “day of Serb determination”.
“I am proud of the people of Republika Srpska, of all those who came out and voted,” he said in the town of Pale.
Regardless of the result, the referendum has already damaged ethnic relations in Bosnia and, arguably, the credibility of the international officials who still oversee the country.
Bosnian Serb President Milorad Dodik has challenged the authority of the national court, which ruled the 9 January holiday unconstitutional and banned the referendum. He also ignored pressure from the European Union, the international high representative and Serbia.
This defiance has increased fears that Mr Dodik might follow through with his threat to hold a secession referendum.
The high representative has the ability to remove politicians from office if they threaten the terms of the Dayton Peace Agreement. But in recent years those powers have been used only rarely.