The operation foiled a plan to smuggle drugs and weapons from South America to the port of Gioia Tauro in Calabria, officials said.
The raids targeted two mafia crime families, the Gambino of New York and the Ndrangheta from Calabria.
FBI agents travelled to Italy to take part in the raids.
Police said the two-year investigation prevented the delivery to Italy of hundreds of kilograms of cocaine hidden in coconuts and pineapples, as well as heroin and marijuana.
Gioia Tauro, the intended destination of the drugs, is one of Europe's largest shipping ports.
Eight of the arrests were made in New York, and are linked with the Gambino crime family which is believed to have negotiated the deal.
The other 18 people were arrested in Italy are believed to have been involved with the Ndrangheta clan.
Police in the US and Italy say they have arrested 26 people in a joint raid against a new mafia-operated drug trafficking route.