Permanent residents can apply for naturalization as U.S. citizens after five (5) years of permanent residence. However, if the individual obtained permanent residence based on marriage, they may be able to apply after three (3) years of permanent residence. Naturalization applicants must be physically present in the United States for more than half their qualifying time, and they should keep their absences from the United States to under six (6) months.
INA 319(b) Naturalizations
In certain unique situations, permanent residents can bypass the qualifying residence time required for naturalization. For example, permanent residents that are married to a U.S. citizen missionary regularly stationed abroad may apply for naturalization without meeting the continuous residence and physical presence requirements.