The 1990 World Series matched the defending champions and heavily favored Oakland Athletics against the Cincinnati Reds, with the Reds sweeping the Series in four games. It was the fifth 4-game sweep by the National League and second by the Reds after they did it in 1976, as well as the second consecutive World Series to end in a sweep, after the A's themselves did it to the San Francisco Giants in 1989. It is remembered for Billy Hatcher's seven consecutive hits. The sweep extended the Reds' World Series winning streak to nine games, dating back to 1975. This also was the second World Series meeting between the two clubs (Oakland won four games to three in 1972). As of 2016, this remains both teams' most recent appearance in the World Series.

Athletics manager Tony La Russa and Reds manager Lou Piniella were old friends and teammates from their Tampa American Legion Post 248 team.

The Cincinnati Reds won the National League West division by five games over the Los Angeles Dodgers. They set an NL record by staying in first place in the division for the entire season or "wire-to-wire", which had been done only one other time, by the 1984 Detroit Tigers. The Reds then defeated the Pittsburgh Pirates, four games to two, in the National League Championship Series.

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