2026 ICD-10-CM Diagnosis Code C31.1Malignant neoplasm of ethmoidal sinus

ICD-10-CM Codes›C00–D49›C30-C39›C31

ICD-10-CM C31.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C31.1 is a billable ICD-10-CM diagnosis code for malignant neoplasm of ethmoidal sinus. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 11 through 13, 146 through 148. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Head and neck cancers - all other types.

For Medicare Advantage risk adjustment, C31.1 maps to CMS-HCC Category 21 (Lymphoma and Other Cancers) under the V28 model, adding a risk factor of about 0.671 for a community, non-dual, aged beneficiary in payment year 2026.

Code Identity

ICD-10-CM Code
C31.1
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of ethmoidal sinus
Short Description
Malignant neoplasm of ethmoidal sinus
Same as the full description in the CMS dataset.
Parent Code
C31
Malignant neoplasm of accessory sinuses

Code Classification

ChapterC00–D49Neoplasms
SectionC30-C39Malignant neoplasms of respiratory and intrathoracic organs
CategoryC31Malignant neoplasm of accessory sinuses
This CodeC31.1Malignant neoplasm of ethmoidal sinus

Medicare Risk Adjustment (HCC)Billing

C31.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.

CMS-HCC V28 Category (Payment Model)
HCC 21— Lymphoma and Other Cancers
Payment HCC · PY 2026 one of 463 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.671
community, non-dual, aged · ranges 0.493–0.739 across segments
Hierarchy
Superseded by HCC 17, HCC 18, HCC 19, and HCC 20
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 11
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 11 · ESRD (V21): HCC 11 · ESRD (V24): HCC 11
ESRD V21 weights: 0.076 dialysis, 0.284–0.298 functioning graft · ESRD V24 weights: 0.059 dialysis, 0.257–0.362 functioning graft
Part D (RxHCC)
RxHCC 22 — Prostate, Breast, Bladder, and Other Cancers and Tumors
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adenocarcinoma of accessory sinus
  • Adenocarcinoma of ethmoidal sinus
  • Carcinoma of ethmoidal sinus
  • Malignant melanoma of accessory sinus
  • Malignant melanoma of ethmoid sinus
  • Malignant neoplasm of ethmoid sinus
  • Primary adenocarcinoma of accessory sinus
  • Primary adenocarcinoma of ethmoidal sinus
  • Primary carcinoma of ethmoidal sinus
  • Primary malignant neoplasm of ethmoidal sinus
  • Primary squamous cell carcinoma of accessory sinus
  • Primary squamous cell carcinoma of ethmoidal sinus
  • Squamous cell carcinoma of ethmoidal sinus

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO010
Head and neck cancers - all other types
Default principal diagnosis: inpatient Yes · outpatient Yes

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
ethmoid (sinus)C31.1C78.39D02.3D14.0D38.5D49.1
sinus (accessory) › ethmoidalC31.1C78.39D02.3D14.0D38.5D49.1

Patient EducationClinical

Nasal Cancer

Your paranasal sinuses are small hollow spaces around the nose. They are lined with cells that make mucus, which keeps your nose from drying out. The nasal cavity is the passageway just behind your nose. Air passes through it on the way to your throat as you breathe.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert C31.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
160.3 Mal neo ethmoidal sinus
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C31.1Overview

What is the ICD-10 code for malignant neoplasm of ethmoidal sinus?

The ICD-10-CM code for malignant neoplasm of ethmoidal sinus is C31.1 (sometimes written as C311). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is C31.1 (Malignant neoplasm of accessory sinuses) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of ethmoidal sinus on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C31.1 group to?

When malignant neoplasm of ethmoidal sinus is the principal diagnosis on an inpatient stay, it groups to MS-DRG 11, 12, 13, 146, 147, 148, with relative weights from 0.7971 to 5.4541 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C31.1?

Under the General Equivalence Mappings, malignant neoplasm of ethmoidal sinus converts to ICD-9-CM 160.3 (mal neo ethmoidal sinus). The mapping is a direct match.

What HCC is C31.1?

C31.1 (malignant neoplasm of ethmoidal sinus) maps to CMS-HCC Category 21 (Lymphoma and Other Cancers), commonly written as HCC 21, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 11 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 22.

Does C31.1 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, C31.1 adds a risk adjustment factor of about 0.671 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.493 to 0.739 depending on the payment segment). A more severe related category (HCC 17, HCC 18, HCC 19, and HCC 20) supersedes it when both are reported. See the full factor table on the HCC 21 category page.