2027 ICD-10-CM Diagnosis Code E66.811Obesity, class 1

ICD-10-CM Codes›E00–E89›E65-E68›E66

ICD-10-CM E66.811
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

E66.811 is a billable ICD-10-CM diagnosis code for obesity, class 1. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 640 through 641. The code is flagged as a questionable admission, since it rarely justifies inpatient admission on its own. Coders also document this condition as obese class I. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Obesity.

Code Identity

ICD-10-CM Code
E66.811
Billable Status
Yes — Valid for Submission
Code Describes
Obesity, class 1
Short Description
Obesity, class 1
Same as the full description in the CMS dataset.
Parent Code
E66.81
Obesity class

Code Classification

ChapterE00–E89Endocrine, nutritional and metabolic diseases
SectionE65-E68Overweight, obesity and other hyperalimentation
CategoryE66Overweight and obesity
This CodeE66.811Obesity, class 1

Code EditsBilling

Medicare Code Editor checks that affect claim validity for E66.811.

Questionable admission codes
Some diagnoses are not usually sufficient justification for admission to an acute care hospital. For example, if a patient is given code R030 for elevated blood pressure reading, without diagnosis of hypertension, then the patient would have a questionable admission, since elevated blood pressure reading is not normally sufficient justification for admission to a hospital. The following list contains diagnosis codes identified as questionable admission when used.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Obese class I

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to E66.811: its own notes plus those printed at E66 and Chapter 4. A note printed at a category, block or chapter applies to every code under it.

Excludes1

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

From Chapter 4 (E00-E89) Endocrine, nutritional and metabolic diseases applies to 973 codes
  • transitory endocrine and metabolic disorders specific to newborn (P70-P74)

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 E66 Overweight and obesity applies to 10 codes
  • adiposogenital dystrophy (E23.6)
  • lipomatosis dolorosa [Dercum] (E88.2)
  • lipomatosis NOS (E88.2)
  • Prader-Willi syndrome (Q87.11)

Code First

The underlying condition named in the note is sequenced before this code.

From E66 Overweight and obesity applies to 10 codes
  • obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From E66 Overweight and obesity applies to 10 codes
  • code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-)

Notes

General instructions on how these codes are used.

From Chapter 4 (E00-E89) Endocrine, nutritional and metabolic diseases applies to 973 codes
  • All neoplasms, whether functionally active or not, are classified in Chapter 2. Appropriate codes in this chapter (i.e. E05.8, E07.0, E16-E31, E34.-) may be used as additional codes to indicate either functional activity by neoplasms and ectopic endocrine tissue or hyperfunction and hypofunction of endocrine glands associated with neoplasms and other conditions classified elsewhere.

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name E66.811, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming E66.811: they are not reported together with it, unless the two conditions are unrelated.

  • R63.5 Abnormal weight gain
    obesity (E66.-) names E66.-, which includes this code

Code First 1

These codes say to code first a condition named in the note, and E66.811 is one of the conditions named.

  • Z99.3 Dependence on wheelchair
    obesity (E66.-) names E66.-, which includes this code

Use Additional Code 2

These codes say to use an additional code from the note, and E66.811 is one of the codes named.

  • E88.81 Metabolic syndrome and other insulin resistance
    obesity (E66.-) names E66.-, which includes this code
  • O99.21 Obesity complicating pregnancy, childbirth, and the puerperium
    code to identify the type of obesity (E66.-) names E66.-, which includes this code

Code Also 1

These codes say E66.811 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • Z15.2 Genetic susceptibility to obesity
    other obesity (E66.8-) names E66.8-, 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 END009
Obesity
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Obesity

    a status with body weight that is grossly above the recommended standards, usually due to accumulation of excess fats in the body. the standards may vary with age, sex, genetic or cultural background. in the body mass index, a bmi greater than 30.0 kg/m2 is considered obese, and a bmi greater than 40.0 kg/m2 is considered morbidly obese (morbid obesity).

Patient EducationClinical

Obesity

Obesity is a disease that means having too much body fat. It is different from being overweight, which means weighing too much. Both terms mean that your weight is greater than what's considered healthy for your height.

The full article covers:

  • What is obesity?
  • What raises your risk of obesity?
  • How is obesity diagnosed?
  • What health problems can obesity cause?
  • What are the treatments for obesity?

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement E66.811 replaces the following previously assigned code(s):

  • E66.8 - Other obesity
FY 2025AddedAdded to the ICD-10-CM code setEffective October 1, 2024.
FY 2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About E66.811Overview

What is the ICD-10 code for obesity, class 1?

The ICD-10-CM code for obesity, class 1 is E66.811 (sometimes written as E66811). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is E66.811 (Obesity class) a billable code?

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

What MS-DRG does E66.811 group to?

When obesity, class 1 is the principal diagnosis on an inpatient stay, it groups to MS-DRG 641, 640, with relative weights from 0.7864 to 1.3392 depending on complications. Higher weights mean higher Medicare reimbursement.

Does E66.811 justify an inpatient admission?

Not on its own. The Medicare Code Editor lists this code as a questionable admission because obesity, class 1 is not usually sufficient justification for admission to an acute care hospital.

Does E66.811 need an additional code?

When the condition applies, yes. The Use Additional Code note at E66, which applies to E66.811, reads: code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-). The additional code is reported after E66.811.