If you have a green card and stay out of the U.S. for an extended period of time, you could risk losing you residency status.
Legal Permanent Residents (green card holders) can be considered to have abandoned their permanent resident status if they move to another country intending to stay their permanently or remain out of the country for over a year without obtaining a reentry permit or a returning resident visa.
Although LPRs are allowed to stay outside of the U.S. for up to a year, if they remain out of the country for any length of time it could raise suspicion with immigration officers; The LPR could be found to have abandoned his permanent resident status.
LPRs should apply for a reentry visa before they leave the country if they plan to be gone for an extended period of time. This visa is valid for two years, but any length of absence from the U.S., even less than a year, may be considered abandoning permanent resident status. Reentry permits should make it easier to prove that the LPR is returning from a temporary visit abroad, which will greatly increase the chances of reentry.
LPRs may also lose their status if they fail to file their income taxes, declare themselves as a “nonimmigrant” on their tax return, or move and fail to inform the Department of Homeland Security. Male LPRs between the ages of 18 and 26 are also required to register with the Selective Service.