The International Court of Justice says the Preah Vihear temple area disputed by Thailand belongs to Cambodia.
The UN's top court has ruled that the area around a flashpoint ancient temple on the Thai border belongs to Cambodia and that any Thai security forces there should leave.
The International Court of Justice interpreted a 1962 ruling saying that "Cambodia had sovereignty over the whole territory of the promontory of Preah Vihear", Judge Peter Tomka said on Monday.
"In consequence Thailand was under an obligation to withdraw from that territory Thai military or police forces or other guards or keepers who were station there," Tomka said.
At least 28 people have been killed in outbreaks of violence since 2011 over the ownership of the patch of border land next to the 900-year-old Preah Vihear temple.
"It's good enough," said Cambodian Foreign Minister Hor Namhong, who was at the hearing in The Hague.
Last year the ICJ ruled both countries should withdraw forces from around the ancient Khmer temple, which is perched on a clifftop in Cambodia but is more easily accessed from the Thai side.
Cambodia and Thailand finally pulled hundreds of soldiers from the disputed zone in July 2012, replacing them with police and security guards.
Ahead of the ruling by the Netherlands-based ICJ, there were fears the decision would revive nationalist tensions and spark renewed clashes.
Tens of thousands of people were displaced in the 2011 fighting, leading Cambodia to ask the ICJ for an interpretation of an original 1962 ruling.
Thailand does not dispute Cambodia's ownership of the temple, a UNESCO World Heritage site, but both sides laid claim to an adjacent 4.6-square-kilometre piece of land.
Leaders of the two countries appealed for calm before the ruling by 17 international judges.
The court decision is binding and cannot be appealed.
The mood on both sides of the Preah Vihear temple was tense ahead of the verdict, with tourists still allowed to visit the ancient structure via Cambodian territory. But journalists were denied access.
The Cambodian army meanwhile denied local media reports it had sent military reinforcements to the area.
On her Facebook page, Thai Prime Minister Yingluck Shinawatra vowed on Sunday to "consult" with Cambodia after the decision to avoid any conflict, adding her government would make a statement following the verdict.
The ruling, which was broadcast live on Thai television, is fraught with danger for her government, which is already grappling with mass street demonstrations against a controversial political amnesty bill.
The country's opposition is now likely to direct public anger towards Yingluck, whose divisive brother Thaksin is close to Cambodia's strongman premier Hun Sen.
Cambodia has allowed Thaksin - who lives in self-imposed exile to avoid a jail term for corruption - to hold a number of rallies for his "Red Shirt" supporters on its soil.
There are fears a negative verdict for Thailand will increase anger among hardline nationalists.
In a television appeal last week, Hun Sen urged his armed forces to "remain calm and show restraint", adding he had agreed with his Thai counterpart to abide by the ICJ's decision.
The roots of the dispute lie in maps drawn up in 1907 during French colonial rule.