2026 ICD-10-CM Diagnosis Code G40.309Generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus

ICD-10-CM Codes›G00–G99›G40-G47›G40

ICD-10-CM G40.309
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G40.309 is a billable ICD-10-CM diagnosis code for generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 100 through 101. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Epilepsy; convulsions.

Code Identity

ICD-10-CM Code
G40.309
Billable Status
Yes — Valid for Submission
Code Describes
Generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus
Short Description
Gen idiopathic epilepsy, not intractable, w/o stat epi
Parent Code
G40.30
Generalized idiopathic epilepsy and epileptic syndromes, not intractable

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG40-G47Episodic and paroxysmal disorders
CategoryG40Epilepsy and recurrent seizures
This CodeG40.309Generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Absence seizure
  • Action myoclonus renal failure syndrome
  • Atypical absence seizure
  • Childhood absence epilepsy
  • Early-onset Lafora body disease
  • Early-onset spastic ataxia, myoclonic epilepsy, neuropathy syndrome
  • Epilepsy with eyelid myoclonia
  • Epilepsy with generalized tonic-clonic seizures alone
  • Focal to bilateral tonic-clonic epileptic seizure
  • Generalized epilepsy
  • Genetic generalized epilepsy
  • Glomerular disease due to action myoclonus renal failure syndrome
  • Idiopathic generalized epilepsy
  • Infantile neuronal ceroid lipofuscinosis
  • Juvenile absence epilepsy
  • Juvenile myoclonic epilepsy
  • Myoclonic epilepsy in infancy
  • Myoclonic epilepsy with ragged red fibers
  • Neuronal ceroid lipofuscinosis
  • Progressive myoclonic epilepsy
  • Progressive myoclonic epilepsy type 3
  • Progressive myoclonic epilepsy type 5
  • Progressive myoclonic epilepsy type 6
  • Progressive myoclonic epilepsy type 7
  • Progressive myoclonic epilepsy type 8
  • Progressive myoclonic epilepsy type 9
  • Progressive myoclonic epilepsy with dystonia
  • Self-limited familial neonatal epilepsy
  • Self-limited neonatal epilepsy
  • Tonic-clonic epileptic seizure
  • Unverricht-Lundborg syndrome

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Generalized idiopathic epilepsy and epileptic syndromes NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • generalized
        • idiopathic
    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • generalized
        • idiopathic
          • not intractable
    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • generalized
        • idiopathic
          • not intractable
            • without status epilepticus
    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • syndromes
        • generalized
          • idiopathic
    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • syndromes
        • generalized
          • idiopathic
            • not intractable
    • Epilepsy, epileptic, epilepsia(attack) (cerebral) (convulsion) (fit) (seizure)
      • syndromes
        • generalized
          • idiopathic
            • not intractable
              • without status epilepticus

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS009
Epilepsy; convulsions
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Generalized Epilepsy

    a chronic condition characterized by recurrent generalized seizures.

  • Generalized Epilepsy with Febrile Seizures Plus, Type 9|GEFSP9

    a subtype of generalized epilepsy with febrile seizures plus caused by mutation(s) in the stx1b gene, encoding syntaxin-1b.

  • Generalized Epilepsy with Febrile Seizures Plus|GEFS+

    a rare, genetically heterogeneous disorder caused by mutations in the scn1a, gabrg2, gabrd, scn9a, or stx1b genes. it is characterized by early childhood onset febrile seizures, generalized tonic-clonic seizures, absence seizures, myoclonic seizures, and atonic seizures

  • Other Generalized Epilepsy, Intractable, with Status Epilepticus|Other generalized epilepsy, intractable, with status epilepticus

    evidence of other generalized epilepsy, with status epilepticus that does not respond optimally to treatment not specified elsewhere.

  • Other Generalized Epilepsy, Intractable, without Status Epilepticus|Other generalized epilepsy, intractable, without stat epi

    evidence of other generalized epilepsy, without status epilepticus that does not respond optimally to treatment not specified elsewhere.

  • Susceptibility to Idiopathic Generalized Epilepsy-10|EIG10

    an autosomal dominant susceptibility to idiopathic generalized epilepsy-10, caused by mutation(s) in the gabrd gene, encoding gamma-aminobutyric acid receptor subunit delta. mutations in the gabrd are also associated with susceptibility to idiopathic generalized epilepsy-10, generalized epilepsy with febrile seizures plus, type 5, and juvenile myoclonic epilepsy-7.

  • Childhood Absence Epilepsy

    a common generalized epilepsy syndrome occurring in children, characterized by absence seizures of short duration. the cause of the syndrome is presumed to be genetic. genes which are associated with the condition include gabrb3, gabrg2, gabra1, cacna1h, and eca1.

  • Juvenile Myoclonic Epilepsy, not Intractable, without Status Epilepticus|Juvenile myoclonic epilepsy, not intractable, without status epilepticus

    evidence of juvenile myoclonic epilepsy without status epilepticus that responds to treatment.

  • Juvenile Myoclonic Epilepsy, not Intractable, with Status Epilepticus|Juvenile myoclonic epilepsy, not intractable, with status epilepticus

    evidence of juvenile myoclonic epilepsy with status epilepticus that responds to treatment.

  • Juvenile Myoclonic Epilepsy, Intractable, without Status Epilepticus|Juvenile myoclonic epilepsy, intractable, without status epilepticus

    intractable juvenile myoclonic epilepsy which is not associated with an acute, prolonged epileptic crisis.

  • Juvenile Myoclonic Epilepsy, Intractable, with Status Epilepticus|Juvenile myoclonic epilepsy, intractable, with status epilepticus

    evidence of juvenile myoclonic epilepsy, with status epilepticus that does not respond optimally to treatment.

  • Juvenile Myoclonic Epilepsy

    an epilepsy characterized by myoclonic jerks, generalized tonic-clonic seizures, and sometimes absence seizures. it appears during adolescence.

  • Childhood Absence Epilepsy

    a common generalized epilepsy syndrome occurring in children, characterized by absence seizures of short duration. the cause of the syndrome is presumed to be genetic. genes which are associated with the condition are gabrb3, gabrg2, gabra1, cacna1h, gabra1, and gabra5.

  • Juvenile Absence Epilepsy

    a subtype of idiopathic generalized epilepsy, whose manifestations occur around puberty, associated with mutation(s) in the efhc1 gene, encoding ef-hand domain-containing protein 1.

  • Susceptibility to Idiopathic Generalized Epilepsy-15|EIG15

    an autosomal dominant susceptibility to idiopathic generalized epilepsy-15, caused by mutation(s) in the rorb gene, encoding nuclear receptor ror-beta. the condition is characterized by early-onset generalized seizures and may have associated developmental delay.

  • Other Generalized Epilepsy, not Intractable, without Status Epilepticus|Other generalized epilepsy, not intractable, without stat epi

    evidence of other generalized epilepsy without status epilepticus that has some acceptable treatment options not specified elsewhere.

  • Other Generalized Epilepsy, not Intractable, with Status Epilepticus|Other generalized epilepsy, not intractable, with stat epi

    evidence of other generalized epilepsy with status epilepticus that has some acceptable treatment options not specified elsewhere.

Patient EducationClinical

Epilepsy

Epilepsy is a brain disorder that causes people to have recurring seizures. The seizures happen when clusters of nerve cells, or neurons, in the brain send out the wrong signals. People may have strange sensations and emotions or behave strangely. They may have violent muscle spasms or lose consciousness.

Read the full article at MedlinePlus

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

Convert G40.309 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
345.10 Gen cnv epil w/o intr ep
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G40.309Overview

Is G40.309 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does G40.309 group to?

When generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus is the principal diagnosis on an inpatient stay, it groups to MS-DRG 100, 101, with relative weights from 0.9026 to 1.9368 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of G40.309?

Under the General Equivalence Mappings, generalized idiopathic epilepsy and epileptic syndromes, not intractable, without status epilepticus converts to ICD-9-CM 345.10 (gen cnv epil w/o intr ep). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.