2027 ICD-10-CM Diagnosis Code F84.2Rett's syndrome

ICD-10-CM Codes›F01–F99›F80-F89›F84

ICD-10-CM F84.2
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

F84.2 is a billable ICD-10-CM diagnosis code for Rett's syndrome. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 56 through 57. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 26 closely related codes. Coders also document this condition as atypical Rett syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Neurodevelopmental disorders.

F84.2 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 133 for payment year 2027.

Code Identity

ICD-10-CM Code
F84.2
Billable Status
Yes — Valid for Submission
Code Describes
Rett's syndrome
Short Description
Rett's syndrome
Same as the full description in the CMS dataset.
Parent Code
F84
Pervasive developmental disorders

Code Classification

ChapterF01–F99Mental and behavioural disorders
SectionF80-F89Pervasive and specific developmental disorders
CategoryF84Pervasive developmental disorders
This CodeF84.2Rett's syndrome

Medicare Risk Adjustment (HCC)Billing

F84.2 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model, but it maps to payment categories in the other CMS models shown below.

CMS-HCC V28 (Medicare Advantage Payment Model)
Not mapped
no payment category in the model that pays 100% of MA risk scores
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
RxHCC 133 — Anxiety and Other Psychiatric Disorders
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Atypical Rett syndrome
  • Dementia due to genetic disease
  • Dementia due to Rett syndrome
  • Dystonia due to Rett syndrome
  • MECP2 related disorder
  • Rett syndrome

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to F84.2: its own notes plus those printed at F84 and Chapter 5. 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.

From Chapter 5 (F01-F99) Mental and behavioural disorders applies to 872 codes
  • disorders of psychological development

Excludes1

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

  • Asperger's syndrome (F84.5)
  • Autistic disorder (F84.0)
  • Other childhood disintegrative disorder (F84.3)

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 5 (F01-F99) Mental and behavioural disorders applies to 872 codes
  • symptoms, signs and abnormal clinical laboratory findings, not elsewhere classified (R00-R99)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From F84 Pervasive developmental disorders applies to 6 codes
  • any associated medical condition and intellectual disabilities

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name F84.2, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming F84.2: they are not reported together with it, unless the two conditions are unrelated.

  • F84.3 Other childhood disintegrative disorder
    Rett's syndrome (F84.2)
  • Z55 Problems related to education and literacy
    disorders of psychological development (F80-F89) names F80-F89, which includes this code

Excludes2 5

These codes carry an Excludes2 note naming F84.2: its condition is not part of those codes, and both may be reported when the patient has both.

  • F80.1 Expressive language disorder
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • F80.2 Mixed receptive-expressive language disorder
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • F90 Attention-deficit hyperactivity disorders
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • F91 Conduct disorders
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • F94.0 Selective mutism
    pervasive developmental disorders (F84.-) names F84.-, which includes this code

Code First 1

These codes say to code first a condition named in the note, and F84.2 is one of the conditions named.

  • Z91.83 Wandering in diseases classified elsewhere
    autism or pervasive developmental disorder (F84.-) names F84.-, which includes this code

Use Additional Code 1

These codes say to use an additional code from the note, and F84.2 is one of the codes named.

  • Q87.87 Hao-Fountain Syndrome
    pervasive developmental disorders (F84.-) names F84.-, which includes this code

Code Also 3

These codes say F84.2 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • G93.45 Developmental and epileptic encephalopathy
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • QA0 Neurodevelopmental disorders related to specific genetic pathogenic variants
    pervasive developmental disorders (F84.-) names F84.-, which includes this code
  • Z15.1 Genetic susceptibility to epilepsy and neurodevelopmental disorders
    pervasive developmental disorders (F84.-) names F84.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MBD014
Neurodevelopmental disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Rett Syndrome

    an inherited neurological developmental disorder that is associated with x-linked inheritance and may be lethal in utero to hemizygous males. the affected female is normal until the age of 6-25 months when progressive loss of voluntary control of hand movements and communication skills; ataxia; seizures; autistic behavior; intermittent hyperventilation; and hyperammonemia appear. (from menkes, textbook of child neurology, 5th ed, p199)

Patient EducationClinical

Rett Syndrome

Rett syndrome is a rare genetic disease that causes developmental and nervous system problems, mostly in girls. It's related to autism spectrum disorder. Babies with Rett syndrome seem to grow and develop normally at first. Between 3 months and 3 years of age, though, they stop developing and even lose some skills. Symptoms include:

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert F84.2 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
330.8 Cereb degen in child NEC
Approximate The match is approximate rather than exact.

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 F84.2Overview

What is the ICD-10 code for Rett's syndrome?

The ICD-10-CM code for Rett's syndrome is F84.2 (sometimes written as F842). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is F84.2 (Pervasive developmental disorders) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report Rett's syndrome on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does F84.2 group to?

When Rett's syndrome is the principal diagnosis on an inpatient stay, it groups to MS-DRG 57, 56, with relative weights from 1.2835 to 2.2649 depending on complications. Higher weights mean higher Medicare reimbursement.

Is F84.2 a CC or MCC?

CMS lists F84.2 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 26 closely related codes in its exclusion list.

Can F84.2 be reported with F84.5?

Not as a rule. The Excludes1 note on F84.2 lists "Asperger's syndrome (F84.5)". 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).

Does F84.2 risk-adjust for Medicare Advantage payment?

Not for Medicare Advantage: F84.2 maps to no category in the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 133 (Anxiety and Other Psychiatric Disorders).