The disclosure by Yahoo! that it sold less internet advertisingspace in recent weeks has worried investors, driving down the value of the company's stock.
The company said that a down turn in car and financial advertising was to blame for the disappointing results.
Chief executive Terry Semel said advertising revenues were "not growing as quickly as we might have hoped at this point in time".
"Not everything is hunky-dory in Yahoo! land," Jordan Rohan of RBC Capital Markets told the International Herald Tribune.
"Yahoo!'s audience is not growing as fast as it once did."
Yahoo! said it wasn't sure whether the down turn was indicative of deeper problems in the market as a whole or just a problem with a few of its clients.
Analysts predicted further trouble for Yahoo! as it struggles to expand its user base at the rate it has previously enjoyed.