Information Sharing Improvement Act of 2004 - Amends the Federal criminal code, the Fair Credit Reporting Act, the Right to Financial Privacy Act, and the National Security Act of 1947 to authorize the Federal Bureau of Investigation (FBI) to disseminate information relevant to an authorized investigation to protect against international terrorism or clandestine intelligence activities only as provided in guidelines approved by the Attorney General (currently, only for foreign intelligence collection or foreign counterintelligence investigations and only if the information is clearly relevant to another agency's authorized responsibilities).

Amends the USA PATRIOT Act to allow the disclosure of counterintelligence or foreign intelligence information obtained as part of a national security investigation (currently limited to a criminal investigation).

Amends rule 6 of the Federal Rules of Criminal Procedure to authorize the disclosure of certain grand-jury information to foreign government personnel. Authorizes: (1) a Government attorney to disclose any grand-jury matter involving specified activities, including a threat of attack, sabotage, terrorism, or clandestine intelligence-gathering, to any appropriate Federal, State, State subdivision, Indian tribal, or foreign government official for the purpose of preventing or responding to such a threat; (2) any State or other specified recipients of information under rule 6 to use the information in accordance with guidelines that the Attorney General and the Director of Central Intelligence jointly issue; and (3) the court to allow disclosure of any grand-jury matter at the request of the Government when sought by a foreign court or prosecutor for use in an official criminal investigation.