New International League Against Epilepsy (ILAE) classification of focal cortical dysplasia (FCD) has introduced in 2011. Important differences from classification by Palmini et al. were mild forms of cortical malformations (mMCDs) was excluded in new classification in terms of no mature agreement and new subgroup FCD type III was introduced. This study aimed to focus on the significance and defect of new FCD classification. Method: One hundred six intractable pediatric epilepsy patients who underwent resective surgery and confirmed with cortical malformation by pathological findings. Results: There were 31 subjects with mMCDs by Palmini et al. and 11 had FCD type I, 34 had FCD type IIa, 19 had FCD type IIb, and 11 had FCD type III by new FCD classification. In other words, 31 patients were not classified to any subtype of new classification, but these patients showed comparable degree of epileptogenicity. When we compare the clinical feature of mMCDs with FCD subtypes, the mMCDs showed similar clinical features to FCD type I than FCD type IIa/type IIb. This study showed different degrees of severity of migration patterns in FCD subtypes. Although, patients in FCD subgroups did not differ in age at seizure onset, seizure frequency, or number of antiepileptic drug (AED) trial before surgery. FCD type I, which is commonly regarded as a mild form of FCD, had a comparable degree of epileptogenicity to other subtypes. FCD type IIb showed a notably higher rate of Engel I outcome compared to other pathological groups [FCD type IIb; 16 cases (84%), other pathologies; 32 cases (57%), P=0.034]. Moreover, severe epileptic burden presenting with a high rate of epileptic encephalopathy could be caused by even mild dysplastic pathology, including FCD type I. Among the pathological subtypes, clinical features of FCD type IIb are distinctive and fairly consistent, and they have highest rate of focal epilepsy, excellent surgical outcomes, success of AED discontinuation after surgery, and positive MRI findings. Conclusion: Although mMCDs was excluded in new FCD classification, this study showed that important pathological finding related to comparable degree of epileptogenicity and Engel class I outcome. Thus, we propose that mMCDs should be included in the new classification.