What is an A-Number?
An A-Number, or Alien Registration Number, is the identifier the Department of Homeland Security assigns to a noncitizen. It stays with you for life, across every form you file and every card you are issued, which is why USCIS asks for it again and again.
Checked against USCIS guidance on September 25, 2026. The sources are listed at the end of this page.
6 steps · Checklist
Find and check your A-number
The full list is at the end of the article.
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What an A-number is
USCIS defines the A-Number as "a unique seven-, eight- or nine-digit number that the Department of Homeland Security assigned to an alien". You will also see it written as Alien Registration Number, Alien Number, A# or simply A-Number. They all mean the same thing.
It identifies you, not a filing. A receipt number changes with every application you send; your A-number does not. Once DHS assigns one, it is yours permanently.
The number is tied to your A-file, the record DHS keeps on you. That is the reason it follows you from a work permit to a green card to naturalization.
How many digits, and the leading-zero rule
Older numbers are seven or eight digits; newer ones are nine. Which you have depends on when DHS assigned it, and a shorter number is not a sign that anything is wrong.
Forms and online systems usually want nine digits. USCIS says that if your A-Number is fewer than 9 digits, insert a zero after the "A" — so A12345678 is entered as A012345678.
| Written on your document | Entered in a 9-digit field |
|---|---|
| A012345678 | A012345678 — already nine digits |
| A12345678 | A012345678 — one zero added after the A |
| A1234567 | A001234567 — two zeros added after the A |
The "A" is a prefix, not part of the number. Some fields ask only for the digits.
Who gets an A-number
Not every noncitizen has one. Lawful permanent residents have one, and so does anyone who has filed for a work permit, applied for a green card, been through immigration court, or otherwise opened a file with DHS.
A tourist or short-term visitor usually does not. If you have never filed anything with USCIS and have never been issued a card, you most likely have no A-number yet — and no form should be making you invent one.
Separately, the Immigration and Nationality Act carries a registration requirement. USCIS states that, with limited exceptions, noncitizens 14 or older who were not registered and fingerprinted when applying for a U.S. visa, and who remain in the United States for 30 days or longer, must apply for registration and fingerprinting. Parents and guardians are responsible for registering children under 14, and previously registered noncitizens must re-register within 30 days of turning 14. USCIS warns that failing to comply may result in criminal and civil penalties.
Where to find yours
It is printed on more documents than most people expect: your green card, your work permit, your USCIS notices and your immigrant visa all carry it. Each one puts it in a different place, which is covered in Where to find your A-number.
If the number on your paperwork does not look like the one you remember, read A-number vs. USCIS number vs. receipt number before assuming there is a mistake. Most of the time it is a different number doing a different job.
Why it matters on a form
Putting the wrong number on a form, or leaving it blank when you do have one, is a filing error that costs time. USCIS uses the A-number to attach what you send to the file it already holds on you.
If you genuinely do not have one, or the number USCIS holds is wrong, see No A-number, or the wrong one.
6 steps · Checklist
Find and check your A-number
Work out whether you have an A-number, find it, and write it the way forms expect.
Decide whether you should have one
Permanent residents and anyone who has filed with USCIS or holds a card do; a short-term visitor who has never filed usually does not.
Find it on a document you already hold
Green card, work permit, USCIS notice or immigrant visa.
Count the digits
Seven, eight and nine are all normal.
Pad it to nine digits when a form asks for nine
Insert a zero after the "A": A12345678 becomes A012345678.
Check it against a second document
The same number should appear on every document DHS has issued you.
Keep it somewhere you can reach it
You will be asked for it on every future filing.
Free, and yours to edit — tick items off on the web or in the MyCheck app.
Frequently asked questions
What is an A-Number?
An A-Number, or Alien Registration Number, is the unique seven-, eight- or nine-digit number the Department of Homeland Security assigns to a noncitizen. It identifies you rather than any single application, and it does not change.
Is the A-Number the same as the USCIS number?
They are the same digits. USCIS defines the USCIS Number as a unique 9-digit number listed on the front of green cards issued after May 10, 2010 — it is the A-Number without the "A" prefix.
How many digits is an A-Number?
Seven, eight or nine, depending on when it was assigned. When a form or system asks for nine digits and yours is shorter, USCIS says to insert a zero after the "A" — A12345678 becomes A012345678.
Does everyone have an A-Number?
No. Permanent residents and anyone who has filed with USCIS or been issued a card has one. A short-term visitor who has never filed anything usually does not.
Does my A-Number ever change?
No. It is tied to your DHS file and stays the same across every form you file and every card you are issued, including after you naturalize.
Read more
Sources
MyCheck is not a law firm and this is not legal advice. Every rule on this page is linked to its USCIS source; check the source for your own situation.
