All ICD10 Codes
R99Billable, valid for claims from October 1, 2026

Ill-defined and unknown cause of mortality

chapter 18: Symptoms, Signs and Abnormal Clinical and Laboratory Findings

  • R99 is billable and valid on claims for FY 2027.
  • As a secondary diagnosis it is not a CC or MCC, so it doesn't raise the MS-DRG payment.
  • Doesn't count toward a Medicare Advantage risk score (no HCC in V28).
  • AHRQ's Chronic Condition Indicator classes it as not chronic (an acute or short-term condition).
  • 10,921 US deaths in 2024 had an underlying cause in category R99, per the National Vital Statistics System on CDC WONDER. Death records use WHO ICD-10, so the count is for the whole category.

Also indexed as: Cot death; Crib death; Death; Sudden infant death syndrome; Syndrome, crib death

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Instructional notes

Includes: conditions that are coded here

  • Death (unexplained) NOS
  • Unspecified cause of mortality

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

  • Section I.C.18.h Death NOS (page 77), covers R99

    Use R99 only when a patient is already dead on arrival at the emergency department or facility. It is not used to report a discharge disposition of death.

Other Chapter 18 topics:

Read Section I.C.18 (page 75)

R99 MS-DRG

As the principal diagnosis, R99 groups to MS-DRG 951 (v44.0).

Related conditions

Grouped by AHRQ's Clinical Classifications Software Refined (CCSR), which sorts every diagnosis code into clinically meaningful categories.

R99 is in Other general signs and symptoms (SYM016, its default category), with 58 codes. Others in it:

  • E88.A Wasting disease (syndrome) due to underlying condition
  • R25.2 Cramp and spasm
  • R29.3 Abnormal posture
  • R29.4 Clicking hip
  • R29.6 Repeated falls
  • R29.890 Loss of height
  • R29.891 Ocular torticollis
  • R29.898 Other symptoms and signs involving the musculoskeletal system

Other codes that refer to R99

Notes on these codes point to R99.

  • CH5 Excludes2: symptoms, signs and abnormal clinical laboratory findings, not elsewhere classified (R00-R99)

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.

ICD-9-CM equivalent

Legacy crosswalk from the CMS General Equivalence Mappings (last updated 2018).

  • 798.0 Sudden infant death syndrome (approximate)
  • 799.9 Other unknown and unspecified cause of morbidity and mortality (approximate)
ICD-9 to ICD-10 converter