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M118 Remark Code (Deactivated): Letter to Follow

M118 meant the payer would send a letter with further information about the claim. X12 deactivated it and suggested N202, an alert saying additional information or explanation will be sent separately.

X12 deactivated RARCM118 on January 1, 2011. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: M118 (RARC M118)
Status: Deactivated StoppedJanuary 1, 2011 (in use since January 1, 1997).
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): Could accompany any adjustment; the letter explained the payer's decision.
OA (Other Adjustment): Sometimes used with other adjustments where the detail was left to correspondence.
Official description: Letter to follow containing further information.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What M118 meant

Remark M118 was a pointer to separate correspondence. The remittance could only carry so much, and when the payer needed to explain more, such as requesting records, describing a review, or detailing an overpayment, it used M118 to say a letter was on the way.

What replaced it

X12’s note suggested N202, and N202 remains active as an alert that additional information or explanation will be sent separately. As an alert, it adds context without being the reason for an adjustment; the CARC on the line, such as CO-16, still carries that reason.

If you still see M118

It remained in use into the 2000s, so you may find it in claims from that period. For any “letter to follow” message, match the letter to the claim when it arrives and act on it. If it never arrives, request it, because deadlines in the letter may apply even when you have not received it.

N202 (Alert: Additional information/explanation will be sent separately.): The suggested replacement: alert that additional information or explanation will be sent separately.
CO-16 (Claim/service lacks information or has submission/billing error(s).): Claim lacks information, often the subject of follow-up letters.

M118 FAQ

What should I do while waiting for the letter?

Note the claim and the expected correspondence in your follow-up queue. If nothing arrives within a reasonable time, call the payer and ask for a copy.

Is M118 the same as N202?

They convey the same idea. N202 is written as an alert, meaning it provides information and does not by itself explain an adjustment.

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