Rasmussen's syndrome (RS), also known as Rasmussen's encephalitis (RE), is a progressive, neurological disease which mostly affects children. It starts to manifest at 6 years of age on average and it is characterised by unihemispheric brain atrophy, epileptic seizures, hemiparesis, cognitive deterioration and, if the language-dominant hemisphere is affected, dysphasia. It develops from, seemingly, full health and arises in the time span of a few months into a condition of extremely frequent seizures which progress to epilepsia partialis continua (EPC) or status epilepticus, which are most commonly completely refractory to medication. The original weakness of one side of the body progresses into unilateral hemiplegia and most of the patients end up unable to walk independently, and in a wheelchair or bedbound. The exact cause remains unknown, but it is a fact that RE is an inflammatory disease in which the cerebral inflammatory infiltrate is predominantly made of T cells. RE is diagnosed by clinical examination and characteristic MRI findings, and the criteria, which were proposed in 2005, are helpful in the diagnosis. The treatment consists of antiepileptic drugs, immunotherapy and surgery, hemispherectomy (HS). Out of those three, HS is the only one effective in suppressing obdurate and intractable seizures. Also, HS affects the disease progression and neuropsychological deterioration. RS can be manifested in less characteristic forms, but that is very rare.