Pope Benedict XVI urged crowds in Palermo, Sicily on Sunday to turn their backs on the "deadly path" of mafia membership.
"Do not give in to the temptations of the Mafia," the head of the Roman Catholic Church said to applause from the faithful that organisers said numbered 26,000 young people, gathered in one of Palermo's main squares.
"Do not be scared of confronting evil!" he added.
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"Together you will be a forest of faith," capable of "profoundly renewing your land", he said.
Saints can be role models: Pope
The pope also offered the example of several saints that could act as models for young people in Italy's largest island, which is in the grip of a social and economic crisis.
He paid special tribute to Pino Puglisi, a priest who had worked in a difficult district of Palermo but was assassinated by the Mafia in 1993, and whose beatification is supported on the island.
Earlier in the day Benedict celebrated an open-air mass in the Sicilian capital before tens of thousands of pilgrims, but disappointed anti-Mafia campaigners with an address they felt did not go far enough.
The pope called on Sicilians, dogged by Mafia extortion and intimidation, to be "ashamed of evil, which offends God and man" and for the effects of organised crime to be brought into the open.
Toni Dell'Olio, a leader of Libera, Italy's largest anti-Mafia organisation, welcomed the pope's latest remarks.
"This is exactly what we expected, a clear statement that the Mafia and Christianity are incompatible", he said.
The clergy, he hoped, would "put into practice these statements from the pope".
Anti-mafia groups want firm line
Before the visit to Sicily, anti-Mafia campaigners had called on the pope to deliver a strong condemnation of organised crime.
Benedict's first visit to Sicily since becoming pope in 2005 had raised hopes among campaigners that he would help their struggle against the ever-pervasive Cosa Nostra.
The head of the Roman Catholic Church also urged pilgrims in Palermo's Foro Italico square to have faith, despite the "shortage of jobs, uncertainty about the future, moral and physical suffering, and organised crime" in Sicily.
"I am here to give you a strong incentive not to be afraid to testify clearly to human and Christian values, so deeply rooted in faith and in the history of this land and its people," he said.
Organisers said around 200,000 people had packed into the square and surrounding streets to attend the mass, celebrated by the pope in bright sunshine against the backdrop of the glittering Mediterranean.
"People of Sicily, look to the future with hope," the pope told them. "Live with courage the values of the Gospel to shine a light on good. With the power of God, everything is possible."
The pope arrived at Palermo's Falcone Borsellino airport, named after two judges killed by the Sicilian Mafia in 1992, before travelling through the city in his popemobile.
Residents hung banners from their houses welcoming the pope, but the atmosphere was subdued, in part due to restrictions on movement and a heavy security presence.
After his speeches and just before leaving the island, Benedict made an unscheduled stop en route to the airport to lay a wreath on a monument dedicated to judge Giovanni Falcone, killed by the Sicilian mafia in May 1992.
In 1995, Benedict XVI's predecessor John Paul II -- on the last of his five visits to Sicily -- attacked Mafia killings, saying "no man, no human association, no Mafia can change nor trample under foot the right to life".
Benedict XVI has in the past condemned the Camorra, the dominant organised crime group in Naples. During an open-air mass in the southern city in 2007, he called for "a struggle against all forms of violence".
The Italian Episcopal Conference, the organisation of Italian bishops, issued a report on the Mafia earlier this year, calling it a "real cancer" and "one of the deepest wounds" in Italy's more impoverished southern regions.
