Matteo Messina Denaro disappeared without a trace in 1993 and then became one of the world's most wanted persons.
Denaro is alleged to be behind a number of serious crimes.
Denaro is known, among other things, for having been involved in several deadly bombings in the Cosa-Nostra mafia's war with the Italian state.
In 1993, he is said to have had a decisive role in a bombing attack against monuments and churches in Rome, Florence and Milan.
In total, 10 people died and 106 were injured.
Denaro was sentenced in absentia to life in prison in 2002.
He then went underground and the police have been chasing him ever since but have now been arrested in Palermo, Sicily.
According to Italian media, he was arrested at a private clinic where he was supposed to undergo therapy.
The text is updated