The convictions were thrown out on an unspecified technicality, Italy's ANSA news agency reported.
Those whose convictions were overturned were among 170 people arrested during a massive operation coordinated by state police in the northern Lombardy region in July 2010.
The 'Ndrangheta mafia is based in the southern Calabria region, but is also active in northern Italy and has branches in Germany, other northern European countries, Australia and Canada.
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