[header] How to cancel your costco membership [title] Bring your costco membership card. [step] Costco issues membership cards when customers sign up, and you will need yours to cancel your membership in person. [substeps] Only the primary member of a costco membership can cancel it. 
If you are not the person who started the membership, you will have to get that person to cancel the membership. If you can't find your membership card, you may have to verify your identity at costco with information like your phone number, address, or birthdate.