The last time the Dow Jones Industrial Average, Nasdaq and S&P 500 closed together at new highs was Dec. 31, 1999. The indexes closed at record highs together 131 times from 1986 to 1999, according to Kensho. It's been 4,000 trading days since the last time the triple record high occurred. Based on the performance of the U.S. stock market after the 1999 feat, investors might be wise to proceed with caution. Here's a look at how the stock market performed in the week after a triple record high.
