Serbian ultra-nationalist Vojislav Seselj has been found not guilty of war crimes and crimes against humanity over the Balkan wars in the 1990s.
The UN war crimes court at The Hague said he had neither borne individual responsibility for the crimes, nor known about them nor endorsed them.
Mr Seselj had denied the charges. In his first reaction, he said the court had reached the only verdict possible.
But Croatia's prime minister condemned the verdict as "shameful".
The UN tribunal's prosecutor Serge Brammertz said his office would decide later whether to appeal.
"I'm absolutely convinced that the victims' communities and many people will not be satisfied with this outcome," Mr Brammertz said.
A fading force in Serbia: analysis by Guy Delauney, BBC News, Belgrade
It was billed as a landmark verdict for The Hague Tribunal but Vojislav Seselj was determined his day of judgement should be business as usual and his wish was granted.
He is not just a free man but available to act as the figurehead of his Radical Party in Serbia's forthcoming general election. The unrepentant ultra-nationalists hold rallies which feature fiery rhetoric and, frequently, burning of EU flags. The next such event, on the outskirts of Belgrade, will follow just hours on from the verdict. But there is little support for ultra-nationalism now and Vojislav Seselj's party will be happy just to gain a parliamentary seat in next month's vote, following an electoral wipe-out two years ago.
Journalist Dejan Anastasejovic, a long-standing critic of Mr Seselj, called the acquittal a "deeply flawed outcome of a deeply flawed process" but said there was now very little political support for Mr Seselj and his allies.
Serbia's Prime Minister Aleksandar Vucic said that "in political terms, this particular verdict could not have serious consequences for Serbia".
Vojislav Seselj - key moments
Youngest PhD holder in what is then Yugoslavia; teaches at Michigan and then at Sarajevo universities
Is jailed for two years in 1984 for advocating that Yugoslavia should be replaced with a Serb-dominated entity
Sets up Serbian Radical Party in 1990, elected MP a year later
Breaks with Slobodan Milosevic in 1993 over Bosnian peace plans
Becomes deputy prime minister in 1998 when the Kosovo atrocities escalate
Indicted by ICTY in 2003, surrenders voluntarily
Temporarily released to Belgrade to undergo treatment in 2014
Acquitted of all charges in 2016