Here are the twenty most common surnames for italian families living in Italy:

Rossi
Russo
Ferrari
Esposito
Bianchi
Romano
Colombo
Ricci
Marino
Greco
Bruno
Gallo
Conti
De Luca
Costa
Giordano
Mancini
Rizzo
Lombardi
Moretti

Even if Rossi is the most common last name in Italy (over 68'000 families), the name Mario Rossi (the italian equivalent of John Doe) isn't the most common name; here you find the 7 most common names and surnames:

Giuseppe Russo
Antonio Russo
Antonio Esposito
Giuseppe Rossi
Salvatore Russo
Francesco Russo
Giuseppe Esposito