The National Provider Identifier: What you need to know and do now
by Legal/Regulatory Affairs and Communications Staff
The Medicare program will not require participating providers to use only their National Provider Identifier (NPI) when submitting Medicare claims as of May 23, 2007. Medicare providers may continue temporarily to use their existing identifier numbers (referred to as "legacy numbers" or "UPIN"), or use their NPI, or submit both numbers on their claims. However, private health insurers may require you to use your NPI as of May 23 in submitting all claims, even if you bill using paper claims.
If you don't have your 10-digit NPI yet, you should apply for it immediately.