Black Monday, the largest one-day percentage fall in Dow Jones Industrial Average history, occurred on October 19, 1987.
The Dow Jones Industrial Average fell 508 points, or 22.6 percent, in a single trading session. The decline followed sharp losses in markets across Asia and Europe and quickly became a worldwide financial shock. Although the point loss was smaller than later crashes, the percentage decline remains the key comparison.
Several forces contributed, including rising interest rates, worries about trade and the dollar, stretched share valuations, and computerized portfolio-insurance selling. That automated selling could accelerate a decline by placing more sell orders as prices fell.
Black Monday is often confused with the Wall Street Crash of 1929, whose most famous panic days were October 24 and October 29. The 1987 crash did not produce a depression, and regulators later introduced circuit breakers designed to pause trading during exceptionally sharp falls.