Isolated hemimegalencephaly (iHME) is a rare form of congenital malformation of cortical development characterized by enlargement of all or part of one cerebral hemisphere. It typically presents with intractable seizures, developmental delay, contralateral hemiparesis, and hemianopia. We report a case of an 18-month-old girl who presented first with focal seizures at tenth day of life, with no other physical or behavioral abnormality. Initial EEG showed excessive sharp EEG transients more over the right hemisphere; repeated EEG showed spikes, polyspikes, sharps, and slow wave discharges predominately over the right hemisphere. MRI of the brain showed asymmetric enlargement of the right cerebral hemisphere, suggestive of hemimegalencephaly. Initial treatment with antiepileptic drugs (AEDs) was successful in controlling her seizures, but later on the seizures became intractable even on polytherapy of AEDs; finally, functional hemispherectomy was performed and she became seizure free. Identification of this and similar cases of iHME can help us to better understand this disorder and eventually to provide better treatment options for it.