R99 — Ill-defined and unknown cause of mortality
Is R99 billable?
Yes — R99 is billable for FY2027. R99 is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. R99 may be submitted for encounters from October 1, 2026 through September 30, 2027.
R99 at a glance
| Code | R99 |
|---|---|
| Description | Ill-defined and unknown cause of mortality |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does R99 group to?
R99 sits in MDC 23 and helps define the logic of 1 MS-DRG (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 951Other Factors Influencing Health Statusmedical
How is R99 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to R99. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Cot death
- Crib death
- Death (cause unknown) (of) (unexplained) (unspecified cause)
- Sudden infant death syndrome (SIDS)
- Syndrome › crib death
Inclusion terms
Alternative wording in documentation that is classified to R99.
- Death (unexplained) NOS
- Unspecified cause of mortality
Excludes2 — not included here — inherited from Chapter 18
The conditions below are not part of R99, but a patient may have both at the same time. When documentation supports it, R99 and the excluded code may both be reported.
How long has R99 existed?
R99 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.