Y09 ICD-10-CM Code: Assault by unspecified means

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for Y09 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on Y09 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for Y09

MedCoder structured workflow — derived from this code’s own official record

Before you code Y09

1. Unspecified does not mean incorrect. When the record gives no greater specificity, Y09 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

   See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

2. An external cause code is reported in addition to the code for the injury or condition, never as the principal or first-listed diagnosis. Confirm the cause, intent, place of occurrence, activity and status where the record documents them, and assign the 7th character that matches the injury code. External cause coding guidelines (Guidelines I.C.20.a).

3. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with Y09. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the record document the detail a more specific sibling code needs?
   Yes → Review the specific siblings in this subcategory.
   No → Continue — Y09 is appropriate when the documentation goes no further.
2. Does the documentation support a condition named in Y09’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewY35, Y36, Y38

Consider Y09. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Any detail beyond this code’s title

What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

• Excludes1 — check before selecting Y09(3 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with Y09: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareY35, Y36, Y38

  See the official tabular notes · Guidelines I.A.12.a

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Indexed As (6)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Circumstance phrases from the official ICD-10-CM External Cause of Injuries Index that map to this code.

• Assault (homicidal) (by) (in)
• Assault (homicidal) (by) (in), injury
• Assault (homicidal) (by) (in), violence
• Assault (homicidal) (by) (in), weapon
• Assault (homicidal) (by) (in), wound
• Injury, injured NOS (accidental(ly)), homicide

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Don’t confuse Y09 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of Y09 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• Y35— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of injuries due to legal intervention moves the case to Y35; the two are not reported together unless documented as unrelated.

  Full comparison: Y09 vs Y35 →

• Y36— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of injuries due to operations of war moves the case to Y36; the two are not reported together unless documented as unrelated.

  Full comparison: Y09 vs Y36 →

• Y38— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of injuries due to terrorism moves the case to Y38; the two are not reported together unless documented as unrelated.

  Full comparison: Y09 vs Y38 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• Principal-diagnosis restriction. External cause of morbidity codes (V, W, X and Y) describe the circumstance that caused an injury, not the condition treated. The Medicare Code Editor rejects them as a principal diagnosis; sequence the injury or condition first and report this code as secondary.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Clinical classification (AHRQ CCSR):EXT019 — External cause codes: unspecified mechanism; EXT022 — External cause codes: intent of injury, assault.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (External cause codes: unspecified mechanism, External cause codes: intent of injury, assault).

R45.88 — Nonsuicidal self-harm, T14.91 — Suicide attempt, T14.91XA — Suicide attempt, initial encounter, X58.XXXA — Exposure to other specified factors, initial encounter, Y35.899A — Legal intervention involving other specified means, unspecified person injured, initial encounter, Y35.91XA — Legal intervention, means unspecified, law enforcement official injured, initial encounter, Y35.92XA — Legal intervention, means unspecified, bystander injured, initial encounter, Y35.93XA — Legal intervention, means unspecified, suspect injured, initial encounter, Y35.99XA — Legal intervention, means unspecified, unspecified person injured, initial encounter, Y36.890A — Unspecified war operations occurring after cessation of hostilities, military personnel, initial encounter, Y36.891A — Unspecified war operations occurring after cessation of hostilities, civilian, initial encounter, Y36.90XA — War operations, unspecified, initial encounter, Y37.90XA — Military operations, unspecified, initial encounter, Y38.80XA — Terrorism involving unspecified means, initial encounter, +488 more

Contextual Map

Every relationship of Y09 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run Y09 with these 3 related codes in Claim Check

Hierarchy

• V00-Y99 — Chapter 20: External Causes of Morbidity (V00-Y99) (V00-Y99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• X92-Y09 — Assault[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Excludes1

• Y35 — Legal intervention[Excludes1]: “injuries due to legal intervention (Y35.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• Y36 — Operations of war[Excludes1]: “injuries due to operations of war (Y36.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• Y38 — Terrorism[Excludes1]: “injuries due to terrorism (Y38.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• EXT019 — External cause codes: unspecified mechanism[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)
• EXT022 — External cause codes: intent of injury, assault[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

External cause index

• Assault (homicidal) (by) (in)[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Assault (homicidal) (by) (in), injury[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Assault (homicidal) (by) (in), violence[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Assault (homicidal) (by) (in), weapon[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Assault (homicidal) (by) (in), wound[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026
• Injury, injured NOS (accidental(ly)), homicide[External cause term]— CMS External Cause of Injuries Index · icd10cm-fy2026

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Coding guidelines Official source data

ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates