Pelosi, a former House speaker, had been scheduled to hold talks with Italian officials, including the defense minister, but the ANSA news agency said she was briefly hospitalized at Rome's Policlinico and then released.
ANSA said that the 70-year-old suffered a minor ailment and underwent tests before being released and going back to her Rome hotel. No further details were given.
The U.S. Embassy in Rome declined comment. Pelosi's office in Washington repeatedly refused requests Monday for information.
ANSA said that Pelosi might still attend an afternoon concert in the Italian parliament marking Italy's 150th anniversary as a united nation.