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ICD-10-CM 2027 diagnosis code

E66.01Morbid (severe) obesity due to excess calories

✓ Billable / specific

E66.01 is a valid, billable ICD-10-CM code for morbid (severe) obesity due to excess calories. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About E66.01

E66.01 is the ICD-10-CM diagnosis code for Morbid (severe) obesity due to excess calories. It belongs to category E66 (Overweight and obesity), block E65-E68 (Overweight, obesity and other hyperalimentation) and chapter 4 (endocrine, nutritional and metabolic diseases). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within E66.0 (obesity due to excess calories), E66.01 is specifically for Morbid (severe) obesity due to excess calories. Related codes cover other obesity due to excess calories (E66.09).

Don't report E66.01 together with the conditions in its Excludes1 note: morbid (severe) obesity with alveolar hypoventilation (E66.2).

Code first: obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-).

Use an additional code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-).

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

In MS-DRG v44.0, it is part of the grouping logic for DRG 640 (Miscellaneous Disorders of Nutrition, Metabolism, Fluids and Electrolytes with MCC, relative weight 1.3395) and DRG 641 (Miscellaneous Disorders of Nutrition, Metabolism, Fluids and Electrolytes without MCC, relative weight 0.7865), in MDC 10 (Endocrine, Nutritional and Metabolic Diseases and Disorders), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 278.01 (Morbid obesity).

Coding notes

Excludes1Not coded here — never report together with this code
  • morbid (severe) obesity with alveolar hypoventilation (E66.2)

Notes that apply from higher levels

Instructions written at a parent level also apply to E66.01.

› From E66 Overweight and obesity
Excludes2
  • adiposogenital dystrophy (E23.6)
  • lipomatosis dolorosa [Dercum] (E88.2)
  • lipomatosis NOS (E88.2)
  • Prader-Willi syndrome (Q87.11)
Code first
  • obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-)
Use additional code
  • code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-)

Broader instructions also apply from Chapter 4: Endocrine, nutritional and metabolic diseases.

Alphabetic index entries

5 entries

Terms in the official ICD-10-CM index that lead to E66.01.

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

ICD-9-CM equivalent

Converter →
  • 278.01Morbid obesityapproximate

From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about E66.01

Is E66.01 billable?

Yes. E66.01 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can E66.01 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict E66.01 as a principal diagnosis.

Is E66.01 a CC or MCC?

No. E66.01 is neither a CC nor an MCC under MS-DRG v44.0.

What DRG does E66.01 group to?

E66.01 is used in the MS-DRG v44.0 logic for MS-DRG 640 (Miscellaneous Disorders of Nutrition, Metabolism, Fluids and Electrolytes with MCC) and MS-DRG 641 (Miscellaneous Disorders of Nutrition, Metabolism, Fluids and Electrolytes without MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.

What is the ICD-9 code for E66.01?

The CMS General Equivalence Mappings map E66.01 to ICD-9-CM 278.01.