May same-restaurant sales were up 2.8 percent in the United States, helped by new coffee drinks and snacks, but that was significantly slower than the 6.1 percent growth in April.
Analysts said the average of estimates called for May growth of around 3.6 percent.
U.S. missed consensus... thus the weakness today, said Stifel Nicolaus analyst Steve West, who added that the U.S. result for May matched his own view.
The results topped Telsey Advisory Group's call for a rise of 2 percent, but missed RBC Capital Markets' expectation that sales could rise 3.9 percent for the month.
McDonald's is one of the restaurant industry's top performers largely because its Dollar Menu has been attracting diners amid a lengthy recession that has sent unemployment sharply higher.
Shares in McDonald's were down 2.7 percent to $58.25 in early afternoon trade. Shares of rival Burger King Holdings Inc
McDonald's faced a tough sales comparison versus a year ago May when McDonald's was giving away Southern Style Chicken sandwiches with a beverage purchase in the United States, Telsey analyst Tom Forte said.
He added that some of the sell-off also could be due to disappointment that sales related to the official McCafe launch failed to drive stronger results.
It's certainly a significant item, but it's not going to move the needle to too large of an extent in any individual month, Forte said.
I do not at all read the number on May as any indication that McCafe is not doing well, he said.
GLOBAL SALES RISE
Worldwide same-restaurant sales, which excludes currency effects, grew 5.1 percent in May, on strong demand from Europe and Asia/Pacific.
However, the growth was down from April, when global same-store sales rose 6.9 percent.
The stronger U.S. dollar -- which lessens the dollar value of overseas sales -- led to an overall 0.4 percent decline in systemwide sales at McDonald's restaurants globally, the company said. Sales rose 7 percent in constant currencies.
McDonald's May same-store sales increased 7.6 percent in Europe, and 6.4 percent in the company's Asia/Pacific, Middle East and Africa segment. In April, same-store sales in the two regions were up 8.4 and 6.5 percent, respectively.
McDonald's said the hit from foreign exchange rates, if they remain around current levels, is expected to be 8 cents to 9 cents a share in the second quarter and about 20 cents for the year. Its prior forecast called for a currency-related drag of 32 cents per share in 2009.
The company also said second-quarter results, which it is scheduled to report on July 23, are expected to include 2 cents to 3 cents a share of income due to a license deal in Indonesia and the sale of Redbox Automated Retail.
(Reporting by Ben Klayman and Lisa Baertlein in Los Angeles; Editing by Maureen Bavdek and Tim Dobbyn)