2026 ICD-10-CM Diagnosis Code I66Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction

ICD-10-CM Codes›I00–I99›I60-I69›I66

ICD-10-CM I66
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I66 is a non-billable ICD-10-CM category code for occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction, so it cannot be submitted on claims. Use a more specific code from this category instead, such as I66.01, I66.02, I66.03, and I66.09.

Code Identity

ICD-10-CM Code
I66
Billable Status
No — Non-Billable Category
Code Describes
Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
Chapter
I60-I69
Cerebrovascular diseases

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI60-I69Cerebrovascular diseases
CategoryI66Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction
This CodeI66Occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction

Specific Coding for Occls and stenosis of cereb art, not rslt in cerebral infrcOverview

Non-specific codes like I66 require more characters. Use one of these billable codes instead:

  • I66.0 for Occlusion and stenosis of middle cerebral artery

  • Use I66.01 for Occlusion and stenosis of right middle cerebral artery

  • Use I66.02 for Occlusion and stenosis of left middle cerebral artery

  • Use I66.03 for Occlusion and stenosis of bilateral middle cerebral arteries

  • Use I66.09 for Occlusion and stenosis of unspecified middle cerebral artery

  • I66.1 for Occlusion and stenosis of anterior cerebral artery

  • Use I66.11 for Occlusion and stenosis of right anterior cerebral artery

  • Use I66.12 for Occlusion and stenosis of left anterior cerebral artery

  • Use I66.13 for Occlusion and stenosis of bilateral anterior cerebral arteries

  • Use I66.19 for Occlusion and stenosis of unspecified anterior cerebral artery

  • I66.2 for Occlusion and stenosis of posterior cerebral artery

  • Use I66.21 for Occlusion and stenosis of right posterior cerebral artery

  • Use I66.22 for Occlusion and stenosis of left posterior cerebral artery

  • Use I66.23 for Occlusion and stenosis of bilateral posterior cerebral arteries

  • Use I66.29 for Occlusion and stenosis of unspecified posterior cerebral artery

  • Use I66.3 for Occlusion and stenosis of cerebellar arteries

  • Use I66.8 for Occlusion and stenosis of other cerebral arteries

  • Use I66.9 for Occlusion and stenosis of unspecified cerebral artery

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Includes

  • embolism of cerebral artery
  • narrowing of cerebral artery
  • obstruction (complete) (partial) of cerebral artery
  • thrombosis of cerebral artery

Type 1 Excludes

  • Occlusion and stenosis of cerebral artery causing cerebral infarction I63.3 I63.5

Patient EducationClinical

Brain Diseases

Your brain is the control center of your body. It controls your thoughts, memory, speech, and movement. It regulates the function of many organs. It's part of your nervous system, which also includes your spinal cord and peripheral nerves. The nervous system sends signals between your brain and the rest of the body.

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 I66Overview

Is I66 a billable code?

No. This is a category header that groups the codes for occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction, and headers cannot be submitted on claims. Claims for occlusion and stenosis of cerebral arteries, not resulting in cerebral infarction need a more specific code from this category, such as I66.01, I66.02, and I66.03.