2026 ICD-10-CM Diagnosis Code C31Malignant neoplasm of accessory sinuses

ICD-10-CM Codes›C00–D49›C30-C39›C31

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

C31 is a non-billable ICD-10-CM category code for malignant neoplasm of accessory sinuses, so it cannot be submitted on claims. Use a more specific code from this category instead, such as C31.0, C31.1, C31.2, and C31.3.

Code Identity

ICD-10-CM Code
C31
Billable Status
No — Non-Billable Category
Code Describes
Malignant neoplasm of accessory sinuses
Short Description
Malignant neoplasm of accessory sinuses
Same as the full description in the CMS dataset.
Chapter
C30-C39
Malignant neoplasms of respiratory and intrathoracic organs

Code Classification

ChapterC00–D49Neoplasms
SectionC30-C39Malignant neoplasms of respiratory and intrathoracic organs
CategoryC31Malignant neoplasm of accessory sinuses
This CodeC31Malignant neoplasm of accessory sinuses

Specific Coding for Malignant neoplasm of accessory sinusesOverview

Non-specific codes like C31 require more characters. Use one of these billable codes instead:

  • Use C31.0 for Malignant neoplasm of maxillary sinus

  • Use C31.1 for Malignant neoplasm of ethmoidal sinus

  • Use C31.2 for Malignant neoplasm of frontal sinus

  • Use C31.3 for Malignant neoplasm of sphenoid sinus

  • Use C31.8 for Malignant neoplasm of overlapping sites of accessory sinuses

  • Use C31.9 for Malignant neoplasm of accessory sinus, unspecified

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.

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 C31Overview

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

No. This is a category header that groups the codes for malignant neoplasm of accessory sinuses, and headers cannot be submitted on claims. Claims for malignant neoplasm of accessory sinuses need a more specific code from this category, such as C31.0, C31.1, and C31.2.