First-Class Catastrophe, A: The Road to Black Monday, the Worst Day in Wall Street History by Diana B. Henriques Monday, October 19, 1987, was by far the worst day in Wall Street history. The market fell 22.6 percent – almost twice as bad as the worst day of 1929 – equal to a one-day loss of nearly 5,000 points today. Black Monday was more than seven years in the making and threatened nearly every U.S. financial institution. ...