2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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
Short Description
Occls and stenosis of cereb art, not rslt in cerebral infrc
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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to I66: its own notes plus those printed at block I60-I69 and Chapter 9. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

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

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

On I66 itself
  • Occlusion and stenosis of cerebral artery causing cerebral infarction (I63.3-I63.5)
From Block I60-I69 Cerebrovascular diseases applies to 410 codes
  • traumatic intracranial hemorrhage (S06.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 9 (I00-I99) Diseases of the circulatory system applies to 1,433 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
  • systemic connective tissue disorders (M30-M36)
  • transient cerebral ischemic attacks and related syndromes (G45.-)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Block I60-I69 Cerebrovascular diseases applies to 410 codes
  • code to identify presence of:
  • alcohol abuse and dependence (F10.-)
  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • hypertension (I10-I1A)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name I66, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming I66: its condition is not part of those codes, and both may be reported when the patient has both.

  • I74 Arterial embolism and thrombosis
    cerebral embolism and thrombosis (I63.3-I63.5, I66.-)

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

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.

Can I66 be reported with a code from S06?

Not as a rule. The Excludes1 note at block I60-I69, which applies to I66, lists "traumatic intracranial hemorrhage (S06.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).