McDonald's Corp on Thursday reported a 1.8 percent drop in October sales at established restaurants around the world, its first monthly sales fall since March 2003, hurt by stiff competition in a weak economy.

Analysts, on average, expected a 1.07 percent decline in sales at restaurants open at least 13 months, according to Consensus Metrix.

The results came just weeks after the world's biggest hamburger chain posted its worst quarterly restaurant sales growth performance in nine years.

October sales at restaurants open at least 13 months fell 2.2 percent in both the United States and Europe and fell 2.4 percent in the Asia/Pacific, Middle East and Africa (APMEA) region.

Analysts, on average, had expected a 1.05 percent decline in the United States, a 0.69 percent fall in Europe and a 3.01 percent drop for the APMEA region, according to Consensus Metrix. The United States just edges out Europe as McDonald's largest market for sales.

McDonald's shares were down 66 cents to $86.20 in premarket trading.

(Reporting By Brad Dorfman in Chicago and Lisa Baertlein in Los Angeles; editing by John Wallace)