Epilepsy is a common manifestation of mitochondrial disease associated with mutations of the mitochondrial polymerase γ (POLG). Prognosis of mitochondrial epilepsy is often poor and there are few reports of successful treatment of POLG-related epilepsy. We describe a 26-year-old woman who experienced severe headache during a three-day period, followed by symptoms of visual flashing, speech difficulty, and generalised seizures. EEG recording showed non-convulsive status epilepticus (left occipital area) and brain MRI revealed parieto-occipital T2-hyperintensities. Visual aura and aphasia persisted despite antiepileptic medication with phenytoin, oxcarbazepine, and levetiracetam. Mitochondrial disorder was clinically suspected and a homozygous c.2243G>C mutation (p.Trp748Ser) was discovered in the POLG1 gene. The patient was then set on a low glycaemic index treatment (LGIT) variant of the ketogenic diet, after which the headaches, aphasia, and visual aura progressively improved and disappeared. She returned home two weeks after onset of symptoms and has not had further seizures. She continues to receive levetiracetam monotherapy and LGIT. We conclude that, at least for this patient, the combination of three antiepileptic drugs and LGIT is effective and well tolerated as treatment for severe episodes of POLG-related mitochondrial epilepsy.