Alleged Sicilian Mafia boss Bernardo Provenzano visited a clinic in the south of France while on the run, Italian media reports say.
Provenzano is reported to have assumed the identity of a baker
The 73-year-old, who evaded police for four decades, underwent surgery in a Marseille clinic in 2003.
DNA analysis of blood samples taken from Provenzano, captured in April, match those held by the clinic.
Provenzano is on trial in the city of Palermo for a series of murders committed during the 1980s.
Italian news agency Ansa says the DNA match provides the first direct proof that Provenzano left Italy and travelled to France during his years on the run.
Earlier in November, a Mafia member close to Provenzano who was said to have organised the trip, was sentenced to more than 13 years in prison.
Some 57 Mafia members close to Provenzano were jailed for a total of 300 years for protecting him while he was in hiding.
Media reports suggest that Provenzano assumed the identity of an Italian baker when he underwent surgery for prostrate cancer in July and October 2003.
Now held in isolation at a high security jail in Terni, central Italy, he was arrested in April at a small farmhouse near his home town of Corleone in Sicily.
Before his capture he had already been convicted in absentia of more than a dozen murders, and 10 more arrest warrants are being re-examined.