Black Monday, the biggest one-day percentage fall in the Dow Jones Industrial Average, occurred on October 19, 1987.
The Dow Jones Industrial Average fell 508 points, or 22.6%, during that session. The percentage loss remains the index's largest single-day decline, although later crashes produced large point losses because the index had grown much higher.
The sell-off spread rapidly through international markets. Hong Kong markets fell first, followed by Europe and the United States. Program trading, portfolio insurance, high valuations, and investor anxiety are among the factors studied as contributors.
Black Monday is often confused with the 1929 Wall Street crash, whose most famous session was Black Tuesday. It also differs from the 1987 crash's broader period of volatility, which continued after October 19.