Chief Executive Officer Marissa Mayer and general counsel Ron Bell released the information Monday in a statement titled "Our Commitment to Our Users' Privacy."
The executives said between 12,000 and 13,000 requests had been received between Dec. 1 and May 31 dealing with criminal, foreign intelligence and other matters.
Most of the requests concerned investigations into criminal matters such as fraud, homicides and kidnappings, the statement said.
Federal law prohibits Yahoo! from identifying the specific number of requests made under the Foreign Intelligence Surveillance Act, Mayer and Bell said, "however, we strongly urge the federal government to reconsider its stance on this issue."
The company said it plans to issue more reports in the future.
"Democracy demands accountability," they said. "Recognizing the important role that Yahoo! can play in ensuring accountability, we will issue later this summer our first global law enforcement transparency report, which will cover the first half of the year."