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N66 Remark Code (Deactivated): Documentation Issue

N66 meant documentation for the claim was missing, incomplete, or invalid. X12 deactivated it and suggested N29 or N225, which were themselves retired in favor of remarks that name the specific document.

X12 deactivated RARCN66 on February 5, 2005. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: N66 (RARC N66)
Status: Deactivated StoppedFebruary 5, 2005 (in use since January 1, 2000).
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): Paired with CO documentation denials; the provider had to supply acceptable records.
Official description: Missing/incomplete/invalid documentation.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N66 meant

Remark N66 was the earliest of the general documentation remarks. It covered any problem with records: none sent, some missing, or what was sent was not acceptable. The provider had to find out from the payer what was wrong.

What replaced it

X12’s note suggested N29 or N225. N29 handled missing documentation and N225 handled incomplete or invalid documentation. Both were later retired once remarks naming specific documents were approved. At the adjustment level, CO-251 says the documentation received was deficient, and CO-252 says documentation is required.

If you still see N66

It only appears in older remittances. When working a similar documentation denial, identify the exact record the payer needs, confirm it is complete and signed, and submit it through the payer’s attachment process with the claim reference.

N29Deactivated (Missing documentation/orders/notes/summary/report/chart.): Suggested replacement for missing documentation, later deactivated.
N225Deactivated (Incomplete/invalid documentation/orders/notes/summary/report/chart.): Suggested replacement for incomplete or invalid documentation, later deactivated.
CO-251 (The attachment/other documentation that was received was incomplete or deficient.): The documentation received was incomplete or deficient.
CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): An attachment or other documentation is required to adjudicate the claim.

N66 FAQ

Why did documentation remarks change twice?

N66 was split into N29 for missing documents and N225 for incomplete or invalid ones. Later, X12 approved remarks for specific document types, and the general ones were retired.

How do I know what document to send today?

Look for a document-specific remark on the remittance, or a request letter. If neither is clear, call the payer before sending records.

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