An Alien Registration Number (A-Number) is a unique 7- to 9-digit number assigned by the Department of Homeland Security to noncitizens in the United States. If you are filling out Form I-9 — either as an employee completing Section 1 or as an employer recording documents in Section 2 — you need to know what the A-Number is, where to find it on immigration documents, and which field it belongs in. Getting this wrong is one of the most common I-9 errors found in audits.
This guide covers where the A-Number appears on every relevant document, how it differs from the USCIS Number and the Document Number, and exactly where it goes on Form I-9.
An Alien Registration Number — also called an A-Number or Alien Number — is a unique identifier that DHS assigns to noncitizens who have records in the U.S. immigration system. The number is 7 to 9 digits long and is always preceded by the letter "A" (for example, A-123456789).
DHS assigns A-Numbers to:
The A-Number stays with the person for life. It does not change when a document is renewed, replaced, or reissued. If someone gets a new green card, a new EAD, or a new approval notice, the A-Number on every document will be the same.
The A-Number appears on several immigration documents. Here is where to look on each one:
| Document | Where the A-Number Appears | Format |
|---|---|---|
| Permanent Resident Card (Form I-551 / Green Card) | Front of the card, labeled "USCIS#" (U.S. Citizenship and Immigration Services) or "Alien #" | A + 7 to 9 digits |
| Employment Authorization Document (Form I-766 / EAD) | Front of the card, labeled "USCIS#" | A + 7 to 9 digits |
| Approval Notice (Form I-797) | Upper left area, near the receipt number | A + 7 to 9 digits |
| Immigrant Visa (passport stamp) | Printed on the visa page in the passport | A + 7 to 9 digits |
| I-551 Stamp (ADIT stamp) | Stamped in the passport or on a Form I-94 | A + 7 to 9 digits |
The A-Number is labeled "USCIS#" on the front of the card. The Document Number is on the back.
On the EAD, both the A-Number (USCIS#) and the Card Number appear on the front of the card. Read the labels carefully to make sure you record the right number.
For a complete guide to how the EAD works on Form I-9 — including expiration rules, auto-extensions, and receipt rules — see our EAD Card guide.
Tip: If the number on your document starts with the letter "A" followed by 7 to 9 digits, that is your A-Number. If you see a 13-character alphanumeric code, that is a Document Number — a different identifier that belongs in a different field on Form I-9. For more on the difference, see our Green Card Number for I-9 guide.
These three numbers cause more I-9 errors than almost anything else. Here is how they differ:
| Number | What It Is | Example | Where on I-9 |
|---|---|---|---|
| Alien Registration Number (A-Number) | Identifies the person. Assigned by DHS. Permanent — never changes. | A-123456789 | Section 1 (employee fills in) |
| USCIS Number | Same as the A-Number, minus the "A" prefix. Same identifier, different format. | 123456789 | Section 1 (same field — either format works) |
| Document Number | Identifies the physical card. Changes every time a new card is issued. | SRC1234567890 | Section 2 (employer fills in) |
The key rule: The A-Number identifies a person. The Document Number identifies a card. They are different numbers, they go in different sections, and they are filled in by different people (employee vs. employer).
In Section 1, the employee attests to their citizenship or immigration status. If the employee selects either of these two options, they must provide their A-Number or USCIS Number:
Lawful permanent residents do not have a choice — they must provide the A-Number or USCIS Number. Aliens authorized to work can provide any one of the three identifiers listed above, whichever appears on their documents.
In Section 2, the employer examines the employee's documents and records what they see. The A-Number does not go in the "Document Number" field in Section 2 — that field is for the Document Number on the physical card. On a green card, the Document Number is a 13-character code on the back of the card. On an EAD, both the A-Number and the card number appear on the front — so look carefully at the labels to make sure you are recording the right number.
However, the employer does encounter the A-Number when creating an E-Verify case. When submitting a case through E-Verify, the system asks for the employee's A-Number or USCIS Number — the same number the employee entered in Section 1.
Not sure which number goes where? Our compliance team has 27+ years of I-9 and E-Verify expertise. We review documents, answer questions, and walk you through every section — including remote verification via video call for distributed teams. Schedule a free compliance call.
This is the most common error. The employer sees the A-Number on the front of the green card or EAD and enters it in the Document Number field in Section 2. But the Document Number is a separate identifier. On a green card, the Document Number is a 13-character code on the back of the card. On an EAD, both the A-Number and the Document Number appear on the front of the card — making it even easier to grab the wrong one. The A-Number belongs in Section 1 only.
"Mixing up the A-Number and the Document Number is one of the most frequent errors we see in I-9 audits," says Patricia, Director of Compliance at i9 Intelligence. "On a green card, the A-Number is on the front and the Document Number is on the back — they're in completely different places. But on an EAD, both numbers are on the front of the card, so you really have to read the labels carefully. Employers confuse them constantly because both fields say 'number.'"
The A-Number and the USCIS Number are the same identifier in different formats. If the A-Number is A-123456789, the USCIS Number is 123456789. Either format is acceptable in Section 1 of Form I-9. There is no need to look for a separate "USCIS Number" — it is just the A-Number without the "A."
If an employee selects "A lawful permanent resident" in Section 1, the A-Number or USCIS Number is required — it cannot be left blank. If the employee does not know their A-Number, they should check their Permanent Resident Card, EAD, approval notice, or any other USCIS correspondence. The number appears on every USCIS document associated with their case.
An I-94 Admission Number is an 11-digit number — different from the A-Number. Employees who select "An alien authorized to work" can provide either their A-Number or their I-94 number or their foreign passport number. These go in separate fields on the I-9 form. Do not enter an I-94 number in the A-Number/USCIS Number field.
Not every work-authorized noncitizen has an A-Number. Some nonimmigrant workers (such as H-1B visa holders who have not yet had a petition filed on their behalf, or certain other categories) may have an I-94 number but no A-Number. In Section 1, these employees select "An alien authorized to work" and provide their I-94 Admission Number or Foreign Passport Number instead.
An Alien Registration Number (A-Number) is a unique 7- to 9-digit number assigned by the Department of Homeland Security to noncitizens in the U.S. immigration system. It is preceded by the letter "A" (for example, A-123456789) and stays with the person permanently. It appears on green cards, EADs, approval notices, and other immigration documents.
The A-Number is on the front of the Permanent Resident Card (Form I-551), labeled as "USCIS#" or "Alien #." It is a 7- to 9-digit number starting with "A." Do not confuse it with the Document Number, which is a 13-character code on the back of the card. For a full breakdown, see our Green Card Number for I-9 guide.
Yes. The USCIS Number is the A-Number without the "A" prefix. If your A-Number is A-123456789, your USCIS Number is 123456789. Both refer to the same identifier, and either format is acceptable on Form I-9 Section 1.
It depends on your immigration status. If you select "A lawful permanent resident" in Section 1, you must provide your A-Number or USCIS Number. If you select "An alien authorized to work," you can provide your A-Number, your I-94 Admission Number, or your Foreign Passport Number — whichever you have.
Some work-authorized noncitizens do not have an A-Number. In that case, the employee selects "An alien authorized to work" in Section 1 and provides their Form I-94 Admission Number or Foreign Passport Number and Country of Issuance instead. The A-Number field can be left blank if the employee provides one of the other acceptable identifiers.
If you have questions about alien registration numbers, USCIS numbers, or any other I-9 document question, our compliance team is here. We have handled hundreds of thousands of I-9s and know exactly how to resolve document questions quickly.
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