Traders work on the floor of the New York Stock Exchange (NYSE) in New York City, U.S., Sept. 16, 2026.

The stock market just posted a banner day by nearly any measure on Monday. The Nasdaq Composite surged 2% to a new record. The broader S&P 500 jumped about 1.5% and now sits less than 1% below a new high.

But traders are buzzing about something unhealthy that occurred under the surface.

More stocks fell to new 52-week lows on Monday than rose to 52-week highs in the index. More specifically, 30 S&P 500 stocks hit new lows, while only seven reached fresh highs.

The last time the index advanced at least 1% to within 1% of a new 52-week high as new lows outnumbered new highs was Dec. 21, 1999, a few months before the Dotcom Bubble top. That's according to Jason Goepfert, who founded SentimenTrader and now serves as an adviser at NextGen News.

Prior to that, the only other time in history this dynamic has played out was July 23, 1929, he noted in a post on X.