Last verified: September 30, 2026. Official procedures can change; use the linked agency pages when you file.

What an A-number is

The Alien Registration Number is the identifier INS/USCIS used to tie records to a person. Older documents may format it differently, and a family file can contain cross-references to more than one number.

Where to look first

  • Old INS or USCIS correspondence
  • Alien registration and immigration documents
  • Immigrant visa or permanent-resident records
  • Naturalization-related correspondence
  • The National Archives Catalog, when NARA has the A-File
  • Family papers that quote an INS file or registration number

Search names as well as numbers

NARA’s catalog descriptions can include an A-number, aliases, dates and places of birth, entry information and naturalization details. Search alternate spellings, maiden names and known aliases instead of assuming the modern spelling is the one used in the federal record.

Our case had two related numbers

We found older INS correspondence containing two related A-numbers. Rather than deciding one was a typo, we gave USCIS both and asked that cross-referenced material be located if possible. That was useful because our goal was the complete immigration/naturalization trail, not one isolated form.

Do not publish the number. Treat A-numbers as identifying information. Keep screenshots and public examples redacted even when the underlying historical record is old.

If you cannot find an A-number

Do not invent one. Search the NARA catalog with biographical details. For historical USCIS records, the Genealogy Program’s index-search process is designed for researchers who do not have a valid file-number citation or are unsure what historical USCIS files exist.

Related guides

Repository guide

USCIS vs. NARA

Find the likely custodian after you locate—or fail to locate—the number.

Read guide →Genealogy tools

Ancestry & FamilySearch research

Use genealogy databases to find dates, locations, name variants and record clues.

Read guide →A-File contents

What can be inside an A-File?

Understand what that number can ultimately lead you to.

Read guide →

Official / primary sources

We separate current source-based guidance from our own family’s experience. Agency custody, forms, fees and procedures can change.