CO 111 denial code

Claim adjustment reason code 111. Often reported as CO 111.

Covered only with assignment accepted

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 111 means

The payer will not pay this service unless the provider accepts assignment on the claim.

For some services, the payer only pays when the provider agrees to accept assignment, meaning payment goes to the provider and the provider accepts the payer's allowed amount. The claim showed that assignment was not accepted.

Check the assignment indicator on the claim. Rules about which services require assignment vary by payer and program.

Group codes seen with 111

On a remittance, 111 comes after a group code. These are the ones it is most often reported with:

• CO 111 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The claim was filed as non-assigned for a service the payer requires to be assigned.
• The assignment indicator on the claim was set wrong by default.
• The provider's enrollment status does not allow non-assigned claims for this service.

What to do next

1. Confirm whether the payer requires assignment for this service.
2. Correct the assignment indicator and resubmit if it was set in error.
3. Review your enrollment and participation status with the payer.

Related codes

• 100 (reason code) Payment sent to the patient
• 16 (reason code) Missing information or billing error