PERMCO is a unique permanent identifier assigned by CRSP to all companies with issues on a CRSP file. This number is permanent for all securities issued by this company regardless of name changes. The mnemonics PERMCO and COMPNO are interchangeable. If the value in this field is less than 20,000, CRSP has used the Nasdaq-assigned Company Number, for when the company had an issue trading on The Nasdaq Stock Market(SM). A value over 20,000 indicates that the number was assigned by CRSP.
The PERMNO identifies a firm's security through all its history, and companies may have several stocks at one time.