ALL males in the US, except for those with NONIMMIGRANT status (such as E, F, G, H, L among others), must register for Selective Service with the US Department of Defense, Selective Service between the ages of 18 and 26. This requirement applies to US Citizen, Permanent Resident, and undocumented males. This requirement does NOT apply to females. This registration can be completed on-line at www.sss.gov or by mailing in a registration card available at US Post Offices and other locations.
This is strictly a Registration. The United States does NOT have a draft or mandatory military service.
In order to be able to apply for college and university financial aid for federal grants and loans and for some scholarships, a male under 26 would have to be registered for Selective Service. Otherwise he would not be eligible for the grants and loans. This could include work study programs at a university.
If a permanent resident male under the age of 31 applies for naturalization (US citizenship) and has failed to register for Selective Service—assuming he was a permanent resident between the ages of 18 and 26—his application could be delayed or even denied in some cases. (If the applicant did not know about the registration requirement, his affidavit of explanation would be required.)
KEY: The Selective Service registration is important for all male permanent residents if they became permanent residents before their 26th birthday.