A referendum on the Annan Plan was held in the Republic of Cyprus and the breakaway Turkish Republic of Northern Cyprus on 24 April 2004. The two communities were asked whether they approved of the fifth revision of the United Nations proposal for reuniting the island, which had been divided since 1974. While it was approved by 65% of Turkish Cypriots, it was rejected by 76% of Greek Cypriots. Turnout for the referendum was high at 89% among Greek Cypriots and 87% among Turkish Cypriots, which was taken as indicative of great interest in the issue on the part of the electorates.
The referendum had originally been planned for 21 April, until the UN planners realised it was the anniversary of the coup in Athens in 1967, which set off the chain of events that led to the Turkish invasion of the island in 1974.
Political leaders in the Republic of Cyprus and Greece strongly opposed the plan. Tassos Papadopoulos, president of the Republic of Cyprus, spoke out against the plan in a speech broadcast live on television. Two days before the referendums, Cyprus's biggest party, Progressive Party of Working People, decided to reject the Annan Plan. Greek Prime Minister Kostas Karamanlis decided to maintain a "neutral" position over the plan, but opposition leader George Papandreou of PASOK urged Cypriots to vote in favour, also because the plan had been promoted by his political party while it was still in power and Papandreou had been the Foreign Minister at the time, and had claimed both communities were ready for "a final common agreement". Nevertheless, opinion polls conducted in the Republic of Cyprus over the entire period of the negotiations from start to finish had always shown around 80% opposition to the proposals. Greek Cypriots have not voted uniformly on the Annan Plan. Their voting behaviour was strongly depended on their partisanship and their location.