There is a "coherent and significant connection" between radiation from Vatican Radio aerials and childhood cancer, researchers have said.
The Italian experts looked at high numbers of tumours and leukaemia in children who live close to Vatican Radio transmitters.
The 60 antennas stand in villages and towns near Rome.
The Vatican said it was astonished and would present contrary views to a court in Rome.
Italian courts have been investigating for 10 years whether of an abnormally high number of deaths from cancer among families living near the aerials just north of the Italian capital can be attributed to electromagnetic radiation.
The 300-page report, ordered by the courts and carried out by Italy's most prestigious cancer research hospital, now concludes that there is a connection between radiation and the cancer incidents.
Some 60 huge steel aerials were erected on farmland owned by the Vatican during the last century.
They transmit Vatican Radio programmes around the world on medium and short wave.
However, the technology is now largely obsolete, as Catholic radio stations in many countries rebroadcast Vatican Radio shows after picking them up on the Internet.
In one court case against the Vatican the statute of limitations ran out, but another case is still pending.
The Vatican says it intends to defend its position and claims there is no threat to public health through its transmissions.
People living near the aerials say the radio waves affect TV reception and interfere with many household electronic appliances.