What an Alien Registration Number is

Every immigration form asks for it, most people applying for the first time do not have one, and the two facts cause a lot of anxious searching. USCIS's own glossary defines the Alien Registration Number as a unique seven-, eight- or nine-digit number that the Department of Homeland Security assigned to an alien. It is written as an A-Number, an A#, or, on a green card, as the USCIS number.

What it is for

The A-Number is a file number. Once DHS opens a record on a person, every later action, whether a petition approved by USCIS, an immigrant visa issued by a consulate, or a hearing before an immigration judge, is filed under the same number. That is why it appears across documents from different agencies: the green card, the employment authorization card, the immigrant visa stamp, USCIS receipt and approval notices, and immigration court paperwork all carry it.

Who has one and who does not

A number is assigned when a case is opened, not at the border. People who have applied for a green card, asylum, or certain other benefits have one; so does anyone placed in removal proceedings. Most tourists, students and temporary workers never receive one, because their cases are handled on other identifiers. A person who has only ever held a visitor visa and an I-94 record will not find an A-Number anywhere, and is not missing anything.

The numbers it is confused with

Three other numbers appear on USCIS paperwork and none of them is the A-Number.

• The receipt number on a USCIS notice is thirteen characters: three letters that identify the service center, followed by ten digits. It identifies a single application, not a person.
• The USCIS online account number is twelve digits and belongs to the online account, not the file.
• The card number on the back of a green card is a separate identifier used for verification.

Entering a receipt number in the A-Number field is a common error and can delay a filing, because the systems do not match.

Reading it off a card

On a green card, the number sits on the front, labeled USCIS#. On an employment authorization card it is also on the front. On a USCIS notice it appears in the header block as A#, and on an immigrant visa it is printed in the annotation area. Leading zeros count; a seven-digit number is written with the zeros DHS prints.

If you cannot find it

A person who once had a number, perhaps from a childhood case, can ask USCIS for their own file through a Freedom of Information Act request, which is free and can be filed online. The USCIS records page explains the process. A person who never had one should leave the field blank or write none where the form permits it; inventing a number, or using someone else's, creates a mismatch that follows the file.