Morbid Obesity ICD-10 Code: E66.01

The ICD-10 code for morbid obesity is E66.01 (Morbid (severe) obesity due to excess calories). This code should always be accompanied by a BMI code from the Z68 category when BMI is documented.

Morbid Obesity Definition

Morbid obesity (also called Class III or severe obesity) is generally defined as:

• BMI ≥ 40, OR
• BMI ≥ 35 with obesity-related comorbidities

ICD-10-CM uses the term "morbid (severe) obesity" - either term in documentation supports E66.01.

Required BMI Coding

Per ICD-10-CM guidelines, always add a Z68 BMI code when BMI is documented:

Note: BMI codes can be assigned based on nursing or dietitian documentation, but the obesity diagnosis itself requires provider documentation.

E66 Obesity Code Family

Excludes1: Obesity Hypoventilation Syndrome

Important exclusion: E66.01 has an Excludes1 note for E66.2 (morbid obesity with alveolar hypoventilation). These codes cannot be used together.

If the patient has both morbid obesity AND obesity hypoventilation syndrome (OHS/Pickwickian syndrome), use only E66.2 - it captures both conditions.

Common Coding Scenarios

Scenario 1: Morbid Obesity with BMI 45

Documentation: "Morbid obesity, BMI 45.2. Discussed bariatric surgery options."

Codes:

• E66.01 (Morbid obesity due to excess calories)
• Z68.42 (BMI 45.0-49.9, adult)

Rationale: Code both the morbid obesity and the specific BMI range.

Scenario 2: Severe Obesity with Diabetes

Documentation: "Severe obesity, BMI 42. Type 2 diabetes, insulin-requiring."

Codes:

• E66.01 (Morbid obesity)
• Z68.41 (BMI 40.0-44.9)
• E11.65 (Type 2 diabetes with hyperglycemia) or appropriate diabetes code

Rationale: Code the morbid obesity with BMI, plus any comorbidities managed during the encounter.

Scenario 3: Obesity Hypoventilation Syndrome

Documentation: "Morbid obesity with obesity hypoventilation syndrome. BMI 52."

Codes:

• E66.2 (Morbid obesity with alveolar hypoventilation)
• Z68.43 (BMI 50.0-59.9)

Rationale: Do NOT code both E66.01 and E66.2. Use E66.2 alone for OHS as it includes the morbid obesity.

Scenario 4: Obesity, Unspecified Severity

Documentation: "Obesity. BMI 37."

Codes:

• E66.9 (Obesity, unspecified) - if provider doesn't specify "morbid" or "severe"
• Z68.37 (BMI 37.0-37.9)

Rationale: Cannot code E66.01 without documentation of "morbid" or "severe." BMI alone doesn't determine the code - provider terminology does.

Query Opportunities

Consider querying when:

• BMI ≥40 but documentation says "obesity" without "morbid" or "severe"
• Patient has OHS symptoms but obesity type isn't specified
• BMI not documented but morbid obesity is listed in history

Bariatric Surgery Coding

For bariatric surgery encounters:

• Primary diagnosis: E66.01 (morbid obesity) for elective bariatric surgery
• BMI code: Appropriate Z68 code
• Status post: After surgery, patients may still code obesity if still obese, or use Z98.84 (Bariatric surgery status) for history