US District Judge William Pauley threw out the lawsuit, which related to Omnicom's transfer of digital assets such as Agency.com and Razorfish in 2001 to a new entity called Seneca Investments.
The lawsuit alleged that the move was a deliberate attempt to hide the true state of Omnicom's financial results. It allowed Omnicom to avoid writing down the value of its investments in the assets, which had fallen after the dotcom bust.
The plaintiffs, led by the New Orleans Employees Retirement System, brought their case in 2002 after Omnicom shares dropped in value following a Wall Street Journal report raising questions about the transaction.
However, the judge dismissed the case yesterday, saying that the plaintiffs had not proved that their losses were caused by any alleged misrepresentation by Omnicom.
Lawyers for the plaintiffs said they were considering an appeal.