The reasons for the drop in U.S. visitors include a weak dollar, post-Sept. 11 fears of terrorism and the diplomatic dispute with some European countries over the Iraq war.
In France, the absence of Americans is headline news. Le Monde newspaper summed up it up in a front-page cartoon that shows two French vacationers reclining under a palm tree.
"Let's not exaggerate! I spotted an American," one of them tells his friend. "Lance Armstrong?"
It's overdoing it to say the U.S. cycling hero who dominated this year's Tour de France to clinch his fifth straight victory is the only American around these days.
Some 2.14 million Americans stayed in hotels across France in the first five months of this year, down nearly 30 percent from the same period a year earlier, according to figures provided by the Tourism Ministry. The drop coincides with the diplomatic crisis between France and the United States over Iraq.
Some 12 percent fewer North Americans visited Britain from May to June, and 25 percent less traveled to the popular Swiss resort of Lucerne, officials said.
Italy, meanwhile, reported a 20 percent drop in the number of American tourists in March, while Spanish authorities said nearly 23 percent less traveled to Spain in the first half of this year compared to 2001, before the Sept. 11 attacks.
"The situation is worse than bad," said Christel Bauer, who sells Mozart busts, miniature dolls and T-shirts at her souvenir shop in Vienna's old quarter.
"We used to have so many people I couldn't even run to the bathroom. But now look," she said, gesturing to the empty store. "Do you see any tourists?"
Her complaints were echoed hundreds of miles away in Amsterdam.
"In July and August, the doorbell usually never stops ringing," said Mara Miller, who runs the "My Home" budget hotel, popular with tourists who like to take advantage of Holland's lax cannabis laws.
"It's not ringing," Miller said. "I've never seen it like this. Ever. Not in 10 years: having empty rooms in July, even an empty bed, is unheard of."
But while there is general agreement in the "old Europe" that Americans have become far and few between, explanations for their disappearance vary greatly.
"I do believe the big problem we've had is the Iraq war, following on from Sept. 11," said Ron Goldsmith, an operations controller for the Big Bus Company, which organizes double-decker bus tours of London's major sites.
He said up to half the Americans were riding the bus this year compared to last.
"They are still a bit twitchy about flying," Goldsmith said. "They're still very, very nervous about what's happening" and the persistent threat of terrorism.
Americans who did make the trip, however, mostly blame the weakness of the dollar that has made traveling in Europe more expensive, for keeping their compatriots away. The dollar slid 18 percent against the euro in the first half of this year.
"Frankly, I think it's the dollar," said Tehmina Tannir, 39, of Santa Monica, Calif., watching the ceremonial changing of the guard outside Buckingham Palace. She said she cut back her normal clothing and shoe shopping by 40 percent.
But for the French, who watched the U.S.-led invasion of Iraq with horror and took the brunt of Washington's wrath for opposing the war, the causes go much deeper.
"We simply don't like each other anymore," said Jacques Milbert, a mustachioed Parisian taxi driver. "If the Americans want to stay at home and eat burgers, that's their problem, not ours."
Fury erupted in the United States earlier this year over France's refusal back the invasion of Iraq, in some cases sparking impromptu boycotts of French wine and cheese.
But if some French people claim not to miss the Americans themselves, many certainly miss their generally thick wallets.
"The absence of Americans and the Japanese is really being felt," said Andre Daguin, the head of France's largest hotel owners' union, the UMIH. "July was a write-off."
Hotels along the French Riviera normally filled with Americans have been particularly badly hit, with Nice and Cannes reporting a 12 and 20 percent drop respectively in room occupancies.
"Only the palaces along the Croisette are pulling through thanks to Middle Eastern clients," said Michel Chevillon, of the Cannes hotel owners' union, who like many desperately hopes business will pick up in August.
The Tourism Ministry sought to downplay the impact of the diplomatic spat between Paris and Washington over Iraq, however.
It prefers to cite the coming together of an array of negative domestic factors -- an oil spill that soiled France's Atlantic coast; forest fires that scorched thousands of acres in the south; crippling transport strikes and, finally, the cancellation of summer culture festivals due to walkouts by artists.
Mandy Water, for one, visiting Geneva for a Christian gathering, thinks France's refusal to align itself with the United States over Iraq is reason enough to keep away.
"If it (the gathering) would have taken place in France, I would have stayed home for political reasons," said the 21-year-old Texan.