"Dewey Defeats Truman" was a famously incorrect banner headline on the front page of the first edition of the Chicago Tribune on November 3, 1948. Incumbent United States President Harry S. Truman, who had been expected to lose to Republican challenger and Governor of New York Thomas E. Dewey in the 1948 presidential race, won the election. A delighted Truman was photographed at St. Louis Union Station holding a copy of his premature political obituary. Only a few hundred copies of the paper were published before the Tribune issued a second edition that backed off from proclaiming a winner. The headline is a cautionary tale for journalists about the dangers of being first to break a story without being certain of its accuracy. It is also a caution about allowing editorial preference to cloud judgment; the Tribune had been strongly against Truman throughout the campaign.

The story by reporter Arthur Sears Henning also reported Republican control of the House of Representatives and Senate that would work with President Dewey. Henning wrote "Dewey and Warren won a sweeping victory in the presidential election yesterday. The early returns showed the Republican ticket leading Truman and Vice President Alben W. Barkley pretty consistently in the western and southern states" and added that "indications were that the complete returns would disclose that Dewey won the presidency by an overwhelming majority of the electoral vote."As it turned out, Truman won the electoral vote by a 303-189 majority over Dewey and Strom Thurmond (though a swing of just a few thousand votes in Ohio, Illinois, and California would have produced a Dewey victory), and the Democrats regained control of both the House and the Senate. Truman was handed a copy of the paper and displayed it to a crowd of well-wishers from his train in St. Louis, Missouri.

In later years, the publishers of the Tribune were able to laugh about the blunder. As the 25th anniversary of the 1948 election approached, the Tribune had planned to give Truman a plaque containing a replica of the erroneous banner headline. However, Truman died on December 26, 1972, before the gift could be bestowed.