| Engel Outcome Scale | |
| Class I: Free of disabling seizures | |
| IA | Completely seizure-free since surgery. |
| IB | Non disabling simple partial seizures only since surgery. |
| IC | Some disabling seizures after surgery, but free of disabling seizures for at least 2 years. |
| ID | Generalized convulsions with antiepileptic drug withdrawal only. |
| Class II: Rare disabling seizures (“almost seizure-free”) | |
| IIA | Initially free of disabling seizures but has rare seizures now. |
| IIB | Rare disabling seizures since surgery. |
| IIC | More than rare disabling seizures after surgery, but rare seizures for at least 2 years. |
| IID | Nocturnal seizures only. |
| Class III: Worthwhile improvement | |
| IIIA | Worthwhile seizure reduction. |
| IIIB | Prolonged seizure-free intervals amounting to greater than half the follow-up period, but not less than 2 years. |
| Class IV: No worthwhile improvement | |
| IVA | Significant seizure reduction. |
| IVB | No appreciable change. |
| IVC | Seizure worse. |