The 1999 United States Open Championship was the 99th U.S. Open, held June 17–20 at Pinehurst Resort Course No. 2 in Pinehurst, North Carolina. Payne Stewart won his second U.S. Open and third major championship, one stroke ahead of runner-up Phil Mickelson.

The United States Open Championship, commonly known as the U.S. Open, is the annual open national championship of golf in the United States. It is the third of the four men's major golf championships, and is on the official schedule of both the PGA Tour and the European Tour. Since 1898 the competition has been 72 holes of stroke play, with the winner being the player with the lowest total number of strokes. It is staged by the United States Golf Association (USGA) in mid-June, scheduled so that, if there are no weather delays, the final round is played on the third Sunday. The U.S. Open is staged at a variety of courses, set up in such a way that scoring is very difficult, with a premium placed on accurate driving. As of 2023, the U.S. Open awards a $20 million purse, the largest of all four major championships.