The Dow Jones Industrial Average lost 22.6% on Black Monday, October 19, 1987.
That fall remains the largest one-day percentage decline in the Dow's history. The selling was global: markets in Hong Kong, London, and other financial centers also suffered severe losses. The crash followed a sharp rise in U.S. share prices earlier in the decade.
Several factors were discussed afterward, including international trade tensions, overvalued shares, computerized trading, portfolio insurance, and investor psychology. No single cause completely explains the event. Program trading may have accelerated selling once prices began to fall.
The percentage loss is often confused with the Dow's point losses in later crashes. Because the Dow's numerical level changes over time, percentage comparisons are the clearer measure of market severity.