Sunday's referendum provided a boost for euro opponents in Britain and Denmark, still using their own currencies. The two, along with Sweden, are holdouts to using the currency, which came into circulation in the European Union in 2002. Denmark had rejected the euro in a referendum in 2000.
"We have evidently not been able to firmly establish the European idea among the voters," said Alf Svensson, leader of the opposition Christian Democrats and a euro supporter. "People still seem to believe that we live in a Europe with national borders and national currency, but the reality is something else."
With all votes counted, 56.1 percent of the more than 5.4 million ballots cast were against the euro, while 41.8 percent voted for it. Two percent cast blank ballots. Turnout was 81.2 percent.
The results ran contrary to opinion polls in the final days leading up to the vote, which showed support for the yes side surging in the wake of the stabbing death of Foreign Minister Anna Lindh on Wednesday.
The attack on Lindh, which police said did not appear politically motivated, came during the final stages of campaigning on whether Sweden should join the European Monetary Union.
Lindh was stabbed repeatedly by an unknown assailant as she shopped in an upscale Stockholm department store. She died Thursday after hours of surgery. Police on Sunday released pictures of a possible suspect, but have made no arrests.
Police were seeking 10 people with criminal records and previous offenses, and there were at least two of particular interest, spokeswoman Stina Wessling told The Associated Press.
Prime Minister Goeran Persson said economic problems in the eurozone likely scared off Swedes. "We could have had a referendum at a better time. Europe is in a deep recession," Persson said.
Persson has said the next opportunity for a euro referendum won't be until 2013.
Graham Watson, leader of the Liberal Democrats in the European Parliament, said the vote portended a likely loss of prestige for the Scandinavian country of 9 million and offered a warning to British Prime Minister Tony Blair.
"Continued self-exclusion from the euro will bring a crushing loss of investment and political influence and increased vulnerability to money market turmoil," he said.
Britain's Foreign Office said it respected the Swedish people's decision but that it would not affect Britain's choice.
Blair has said he supports adopting the euro in principle, but only when the economic conditions are right. His government announced in June that it was not time to call a referendum because Britain's economy had not converged enough with that of the 12-nation euro zone.
Despite Sunday's setback, European Union officials were optimistic that Sweden would keep up its push to ditch the national currency, the krona, in favor of the euro.
"We're confident the Swedish government will chose a way forward to keep the euro project alive in Sweden," the EU Commission said in a statement.
Michael Ancram, foreign affairs spokesman for Britain's opposition Conservative Party, which opposes joining the euro, told Sky News that the Swedish outcome "gives the lie to those who've been saying for years, 'Oh, joining the euro is inevitable, and only the British are creating any problems about it.'
The results "strengthen my view that the euro is not for Britain, it's not in our economic interest, it's not in our political interest," he said.
The vote may also raise concern among the newly tapped members of the European Union, including Baltic neighbor Estonia which approved joining the EU in a referendum Sunday.
Next year, the 15-member EU will expand with 10 new members, the Czech republic, Poland, Hungary, Lithuania, Malta, Slovenia, Slovakia, Latvia, Estonia and Cyprus.
Supporters of the single currency contend it will make transnational business and travel easier, free up more money for investment and fuse together the economic fortunes of countries who were once enemies. Opponents believe a single economic policy cannot fit right for more than a dozen countries.