A statement said the graves in the centuries old Teutonic Cemetery would be opened on July 11 in the presence of representatives of the family of Emanuela Orlandi, after the family received an anonymous tip that she might be buried there.
The disappearance in 1983 of Orlandi, then 15, is one of the most enduring modern mysteries of the headquarters of the Catholic Church and has been the subject of wild speculation by Italian media.
Unproven theories over the decades have run the gamut from an attempt to secure the freedom of a gunman jailed for trying to assassinate Pope John Paul II, to a connection to the grave of Enrico De Pedis, a mobster buried in a Rome basilica. His tomb was opened in 2012 but nothing was revealed.
Last year, bones found during ground work at the Vatican embassy in Rome sparked an Italian media frenzy suggesting they might belong to Orlandi or to Mirella Gregori, another teenager who disappeared the same year. DNA tests turned out negative.
The Orlandi family later received an anonymous letter saying Emanuela could be buried in the Teutonic Cemetery, a small burial ground in the Vatican used over the centuries mainly for Church figures of German or Austrian origin.
Police at the time of the disappearance did not exclude that she simply may have been abducted and killed for reasons with no connection to the Vatican or may have been a victim of human trafficking for sexual reasons. She would now be 51.
Laura Sgro, an Orlandi family lawyer, said the family was grateful for the Vatican's decision to open the graves.