It is important to remember that foreign citizens, after renewing their residency permit [permesso di soggiorno], must go to the registrar’s office [Servizi demografici] and confirm their fixed address, which must then be checked by the office [Ufficio Anagrafe] (pursuant to Presidential Decree 223/89, art. 11). This requirement was specified and repeated with the approval of the Ministry of the Interior on 19.11.2004.
Failure to confirm your regular fixed address can cause you to be deleted from the municipal lists of residents; it has to be done within 1 year of the date of expiry of the residency permit, after obtaining the original.
It is therefore advisable to do this as soon as you receive the permit. Generally the municipal offices sends a notice to the foreign citizen to go to the office and confirm the regular address, indicating a term of 30 days.