SB1 resident visa is for a permanent resident returning to the US from a visit abroad of more than one year.  The SB1 resident visa applicant must have stayed outside of the US due to emergency or extraordinary circumstances that prevented the permanent resident from being able to return to the US within the required one year period.

Examples of emergency or extraordinary circumstances would if an SB1 resident visa applicant had been seriously injured in a car wreck, required to work outside the US by an employer or kidnapped by terrorists.  SB1 resident visa applicants must be able to document their specific reason for their extended absence using documents such as medical, employment or police records.

SB1 resident visa applicants must also evidence they have maintained an intent to return to the US.  This can be done using by voting in US elections, maintaining a US residence, maintaining a US bank account, filing US tax returns or payment of US utility bills.  If approved the SB1 resident visa applicant will have their US permanent residence reinstated.

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US State Department - SB1 Resident Visa

Foreign Affairs Manual - SB1 Resident Visa