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ICD-10/I66.9

I66.9 ICD-10-CM Code: Occlusion and stenosis of unspecified cerebral artery

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Inpatient Payment Groups (MS-DRG)

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43.0 (FY2026), Appendix B.

  • MS-DRG 061 — ISCHEMIC STROKE, PRECEREBRAL OCCLUSION OR TRANSIENT ISCHEMIA WITH THROMBOLYTIC AGENT WITH MCC (MDC 01)
  • MS-DRG 062 — ISCHEMIC STROKE, PRECEREBRAL OCCLUSION OR TRANSIENT ISCHEMIA WITH THROMBOLYTIC AGENT WITH CC (MDC 01)
  • MS-DRG 063 — ISCHEMIC STROKE, PRECEREBRAL OCCLUSION OR TRANSIENT ISCHEMIA WITH THROMBOLYTIC AGENT WITHOUT CC/MCC (MDC 01)
  • MS-DRG 067 — PRECEREBRAL OCCLUSION WITHOUT INFARCTION WITH MCC (MDC 01)
  • MS-DRG 068 — PRECEREBRAL OCCLUSION WITHOUT INFARCTION WITHOUT MCC (MDC 01)
  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Code Set: Valid FY2026 and FY2027. FY2026 took effect October 1, 2025.

Official Registry Overview & Definition

Occlusion and stenosis of unspecified cerebral artery is a billable ICD-10-CM diagnosis code (I66.9).

Official Tabular Instructional Notes

Sequencing, inclusion, and exclusion notes published for I66.9 in the official ICD-10-CM tabular list.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

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

Excludes1 — Not Coded Here

Conditions that can never be reported with this code; the two are mutually exclusive.

  • Occlusion and stenosis of cerebral artery causing cerebral infarction (I63.3-I63.5)
  • traumatic intracranial hemorrhage (S06.-)

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional 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)

Nearest Codes in This Family

Official ICD-10-CM classifications closest to I66.9 in its code family, with their registry titles.

  • I66.12 — Occlusion and stenosis of left anterior cerebral artery
  • I66.13 — Occlusion and stenosis of bilateral anterior cerebral arteries
  • I66.19 — Occlusion and stenosis of unspecified anterior cerebral artery
  • I66.2 — Occlusion and stenosis of posterior cerebral artery
  • I66.21 — Occlusion and stenosis of right posterior cerebral artery
  • I66.22 — Occlusion and stenosis of left posterior cerebral artery
  • I66.23 — Occlusion and stenosis of bilateral posterior cerebral arteries
  • I66.29 — Occlusion and stenosis of unspecified posterior cerebral artery
  • I66.3 — Occlusion and stenosis of cerebellar arteries
  • I66.8 — Occlusion and stenosis of other cerebral arteries

View all codes in the I66 family

Indexed Clinical Terms (4)

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code.

  • Occlusion, occluded, artery, brain or cerebral
  • Occlusion, occluded, artery, cerebral
  • Thrombosis, thrombotic (bland) (multiple) (progressive) (silent) (vessel), cortical
  • Thrombosis, thrombotic (bland) (multiple) (progressive) (silent) (vessel), intracranial (arterial)