Ideally, each person has only one Social Security number. When you apply for a number, the identifying information you provide on the application form (your name, date of birth, place of birth and parents' names) is matched against all of Social Security's records to see if you already have a number. If Social Security finds a match, the Social Security Administration’s issue you a replacement card with that number. If Social Security does not find a match, Social Security assigns you a new number. In Social Security's early years, these matches were done manually, and the local Social Security offices typed and issued the cards. Now the matches are done electronically, and Social Security issues the cards from Social Security headquarters in Baltimore, MD.

Over the years, some people have been issued more than one Social Security number. This usually happens when the information entered on one application doesn't match the information on a later application. Perhaps the name is shown differently or a nickname is used, the date of birth or place of birth is not the same, or a stepparent's name is given instead of a birth parent's. Sometimes this happens when a parent gets a number for a young child and the child later fills out an application as part of a school lesson on Social Security. Whatever the cause, if the information on the applications does not match, Social Security may assign a new number.

Social Security also could inadvertently assign more than one number if a person sends in two applications within a very short time. If the first application is not yet processed and on the record when the second one comes in, the system will not be able to identify a match.

When Social Security can determine that more than one number belongs to the same person, Social Security cross-references those numbers in their records. Then when Social Security selects one of the numbers to issue a Statement, Social Security combines the information from all the cross-referred numbers to display the year-by-year earnings and calculate the estimated benefits.

You don't need to take any action about the other numbers shown on your record. You should continue to use the one under which you are currently working. However, if you have more than one number and Social Security has not shown them all on your Statement, you should report this to Social Security so that they can cross-reference the numbers and make sure that you get credit for all your earnings.