Warren Buffett Just Delivered a Fresh Warning to Wall Street. Here's What It Means for Investing Right Now.

Warren Buffett has become an icon in the world of investing, thanks to his excellence in this area decade after decade. As chief executive officer, he led Berkshire Hathaway to 60 years of market-beating performance. Though he retired from that post at the end of 2025, he remains chairman of the holding company, continues to go into the office -- and continues to share his thoughts on investing.

The recent stock market turbulence makes now the perfect time to turn to Buffett for advice. Stocks have swung from gains to losses, amid spikes in volatility, and the S&P 500 finally ended the month of March with a 5% decline. Investors sold off tech stocks and avoided growth stocks in general amid a variety of concerns, including worries about the U.S. economy and the war in Iran.

Against this backdrop, Buffett -- who has been a net seller of stocks for more than a dozen quarters -- delivered a fresh warning to Wall Street. Let's check it out and consider what it means for investing right now.

Image source: The Motley Fool.

The S&P 500's bull market

So, first, it's important to note the S&P 500's performance over the past few years. The index roared into its third year of a bull market in October, and along the way, reached record highs multiple times. In fact, over the past three calendar years, the famous benchmark advanced nearly 80%.

And artificial intelligence (AI) has been one of the principal themes driving the momentum. Investors placed their bets on AI stocks, from chip giant Nvidia to cloud leader Alphabet, and these players have helped set the pace for the overall index. This is because AI has the potential to reshape how many things are done, making companies more efficient and innovative, and therefore this technology could significantly boost corporate earnings.

But over the past several weeks, investors have hesitated to buy these players as general uncertainty weighed on their appetite for growth assets. These types of investments often flourish in strong economic environments -- so today, with concerns about the geopolitical situation, the U.S. economy, and the sustainability of AI growth, investors have grown more hesitant about investing in AI stocks. In fact, many have actually sold or reduced their positions in certain players -- even the biggest of names. Nvidia, for example, slipped 1.5% in March, and this is in spite of the company's positive messages at its GTC conference earlier in the month, and the S&P 500 sank 5%.

Buffett's words about his top holding

Now, let's consider Buffett's warning to Wall Street. In a recent interview with CNBC, the famous investor spoke about Apple (NASDAQ: AAPL) -- Buffett progressively cut his position in the smartphone giant last year, but it remains Berkshire Hathaway's biggest position.

In the interview, he suggested he would buy more Apple shares -- and many of them -- if the price were right. Here's the key point, though: Buffett said he isn't ready to buy Apple "in this market."

"I mean, it just isn't going to happen in this market," Buffett told CNBC.

Buffett didn't specifically say why, but it's reasonable to turn to an element that has clearly limited the billionaire's buying activities in recent quarters, and that's valuation. This investing expert owes many of his successes to the fact that he's a value investor, getting in on stocks when they're trading for less than what they're actually worth.

As the AI boom gathered momentum, it pushed stocks to record valuations, as we can see in the S&P 500 Shiller CAPE ratio, an inflation-adjusted look at stock price in relation to earnings per share.

Here, we can see that valuation has only been this high once before, during the dot-com bubble back in 2000.

S&P 500 Shiller CAPE Ratio data by YCharts

Apple's valuation

Meanwhile, Apple stock may not be excessively expensive, but its valuation hasn't greatly changed over the past few years. So Buffett may not view it as a must-buy right now.

AAPL PE Ratio (Forward) data by YCharts

Buffett's message could be interpreted as the following: The stock market, overall, remains expensive even after last month's decline. Does this mean you should stay away from investing right now? Not necessarily. At what levels are valuations attractive? "It depends on the stock," Buffett said in the CNBC interview.

All of this reinforces the idea that any time could be a good time to invest -- but it's critical to consider valuation before hitting the "buy" button. How should you apply this today? By looking at quality stocks that have underperformed in recent months, and considering whether they might be reasonably priced right now. And when you do find that bargain, it's key to, like Warren Buffett, hold on for the long term.

Adria Cimino has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Alphabet, Apple, Berkshire Hathaway, and Nvidia and is short shares of Apple. The Motley Fool has a disclosure policy.