2026 ICD-10-CM Diagnosis Code S31.65AAOpen bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter

ICD-10-CM Codes›S00–T88›S30-S39›S31

ICD-10-CM S31.65AA
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S31.65AA is a billable ICD-10-CM diagnosis code for open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 393 through 395, 963 through 965. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family.

Code Identity

ICD-10-CM Code
S31.65AA
Billable Status
Yes — Valid for Submission
Code Describes
Open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter
Short Description
Open bite of abd wall, unsp flank with penet perit cav, init
Parent Code
S31.65A
Open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS30-S39Injuries to the abdomen, lower back, lumbar spine, pelvis and external genitals
CategoryS31Open wound of abdomen, lower back, pelvis and external genitals
This CodeS31.65AAOpen bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for S31.65AA.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Open wound of abdomen, lower back, pelvis and external genitals (S31). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Code History & ChangesHistory

New Code S31.65AA was added to the ICD-10-CM code set for FY 2026, effective October 1, 2025.

Replacement S31.65AA replaces the following previously assigned code(s):

  • S31.659A - Open bite of abd wall, unsp quadrant w penet perit cav, init
FY 2026AddedAdded to the ICD-10-CM code setEffective October 1, 2025.
FY 2026CurrentRevised in the current code setEffective October 1, 2025 through September 30, 2026.

Questions About S31.65AAOverview

Is S31.65AA a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S31.65AA mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, such as an emergency visit or first evaluation.

What MS-DRG does S31.65AA group to?

When open bite of abdominal wall, unspecified flank with penetration into peritoneal cavity, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 393, 394, 395, 963, 964, 965, with relative weights from 0.6490 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.