Principal Diagnosis vs First Listed (ICD-10-CM)

Jul 14th, 2026

Are principal diagnosis and first listed diagnosis the same thing in ICD-10-CM coding? The answer is yes and no. The ICD-10-CM Official Guidelines for Coding and Reporting sometimes makes a distinction between “principal diagnosis” and “first listed” diagnosis in many of the instructions. Generally speaking, "first-listed" means that they are referring to outpatient services, whereas "principal diagnoses" applies to the inpatient setting. However, there are other places where these phrases seem to be used interchangeably. For example:

• "principal or first-listed" appears 23 times
• "principal/first-listed" appears 15 times
• "first-listed or principal" appears 9 times

Unless there are specific guidelines (e.g., reporting an unconfirmed diagnosis in an inpatient setting which is allowed; HIV reporting [Section 1;C.1.a]) then the principal diagnosis icons shown in FindACode.com apply to both the inpatient and outpatient setting - unless otherwise noted.