You may not need all of the following documents. Sometimes one document can substitute for another. The lists are not all-inclusive. The Social Security Administration (SSA) will tell you what you need and what other documents are acceptable. They will help you get them if you are having trouble.
SOCIAL SECURITY CARD OR NUMBER
You will need to apply for a Social Security number if you do not have one.
PROOF OF AGE
NOTE: If you already proved your age when you applied for Social Security benefits, you do not need to prove it again for SSI.
CITIZENSHIP OR ALIEN STATUS RECORD
If you are a citizen, examples of documents you may need are:
If you are an alien, examples of documents you may need are:
If you are an alien who has served in the U.S. Armed Forces, you may need your military discharge paper (form DD-214).
PROOF OF INCOME
If you have income, you may need to provide the following:
PROOF OF RESOURCES
PROOF OF LIVING ARRANGEMENTS
MEDICAL SOURCES (If you are filing as blind or disabled)
If you are applying as a disabled child, or on behalf of a disabled child, SSA will need the names, addresses, and telephone numbers of people (teachers, caregivers) who can provide information about how the disabled child's medical condition affects his or her day-to-day activities.
THINGS TO REMEMBER
THIS INFORMATION IS GENERAL. FOR MORE INFORMATION, CALL 1-800-772-1213 (TTY 1-800-325-0778), OR CONTACT YOUR LOCAL SOCIAL SECURITY OFFICE.
Source: Social Security Website: Understanding Supplemental Security Income Home Page