<p>An alien must maintain his permanent residence in the U.S. in order to keep    his permanent residence. If the alien leaves the U.S. for more than a year then    he will lose his permanent residence. A special document called a Permit to    Reenter can be obtained from the Citizenship &amp; Immigration Services Office    and with that document an alien can leave the U.S., and reside in a foreign    country for up to 2 years before returning and still maintain permanent resident    status in the U.S.</p>
<p>There is no specific term of months per year that an alien must stay in the    US in order to keep his green card, however, a repeated pattern or lengthy stays    abroad may jeopardize an alien's permanent residence. Many aliens feel that    if they come to the US once per year for a short period of time they can maintain    their permanent residence. This is not true. If the Citizenship &amp; Immigration    Services Office discovers that the alien comes to the US only once per year,    it is possible that it will initiate proceedings to revoke the alien's green    card.</p>