Effective March 1, 2008, your Medicare FFS claims must include an NPI in the primary provider fields on the claim (i.e., the billing, pay-to provider and rendering provider fields). You may continue to submit NPI/legacy pairs in these fields or submit only your NPI. The secondary provider fields (i.e., referring, ordering and supervising) may continue to include only your legacy number, if you choose. Failure to submit an NPI in the primary provider fields will result in your claim being rejected, beginning March 1, 2008. Also, as of May 23rd, 2008 Medicare will not allow any legacy ID’s on the claims, NPI only, including the referring provider field.