Hemispherectomy is a treatment primarily indicated for intractable epilepsy in children. The first hemispherectomy was performed by Dandy in 1928 during the removal of a tumor, and in 1938 Mckenzie reported the first case of hemispherectomy to treat infantile hemiplegia with intractable epilepsy, after which seizures ceased, behavior improved, and hemiplegia did not worsen. In 1950, Krynauw published a group of 12 cases of infantile paralysis with epilepsy in which hemispherectomy was performed with good results. In the 1950s, Professor Shi Yuquan, a pioneer of modern epilepsy surgery in China, first performed hemispherectomy in Shanghai. Nowadays, many units in China are performing it, and we have completed 7 cases in 2007 alone. The so-called cerebral hemispherectomy is anatomically speaking a cortical resection of the cerebral hemisphere, and the term cerebral hemispherectomy is still customarily used. The main indications for surgery are: 1. Rasmussen syndrome. 2. 2. Infantile hemiplegia with intractable epilepsy and behavioral disorders. 3. Sterge-Weber (cerebral facial hemangioma) syndrome. 4.Megalencephaly on one side. 5.Major vascular occlusion causing damage to one hemisphere with intractable epilepsy. 6.Widespread cortical developmental abnormalities on one side mainly. Caution should be exercised in the presence of independent epileptogenic foci in both hemispheres; bilateral ventricular enlargement; IQ below 60 and severe language impairment; absence of contralateral hemiparesis; and a language center located in the affected hemisphere. A thorough preoperative evaluation is particularly important to select appropriate indications, determine the surgical plan, and minimize and avoid complications. In addition to a detailed history and routine neuropsychological examination, high field strength magnetic resonance imaging (MRI) is now essential to discern structural intracranial changes well. Long-range video EEG should capture more than 2 typical seizures of the patient, and combined with history and MRI performance, a clear diagnosis can be made for the majority of patients. In recent years, with the rapid development of science and technology, more and more functional examinations are being used in clinical practice, which can be reasonably selected according to the condition and economic conditions. Positron emission computed tomography (PET) is currently more often used as a tracer of 18 fluorodeoxyglucose (18FDG), which can help doctors determine the function of both hemispheres and postoperative expectations by responding to the function of brain tissue through glucose metabolism, and newer equipment can scan simultaneously with CT (PET-CT), making up for the relatively low spatial resolution of PET. Magnetoencephalography (MEG) is an absolute measurement of the magnetic field generated by intracellular axial currents. In addition, the skull is transparent to the brain’s magnetic field, and the magnetic field is less affected by other factors. MEG can improve the ability to localize epileptiform activity and is also used to localize major functional areas of the brain. Functional MRI (fMRI) has developed rapidly in recent years and its application fields are becoming more and more extensive. It can not only localize single functional areas such as sensory, motor, language, visual, and auditory, but also is increasingly applied to the study of higher brain functions such as memory and emotion, which can help a lot in determining the residual functions of the diseased cerebral hemisphere, and it is relatively inexpensive and easy to accept. Hemispherectomy has evolved over half a century and the surgical protocols have been continuously improved. The initial approach has been abandoned due to the high number of late complications, mainly hydrocephalus and long-term chronic hemorrhage resulting in iron-containing heme deposits. The existing protocols have been used in different units, and a longer period of time is needed to compare the advantages and disadvantages. Modified cerebral hemispherectomy and functional hemispherectomy are currently being performed, and Delalande et al. were the first to perform hemispherectomy, which preserves the anatomy while leaving the affected hemisphere completely isolated. Modified cerebral hemispherectomy was first performed by Wilson starting in 1969 with general anesthesia, semi-lateral recumbency, and a frontoparieto-occipital curved incision. We mostly use a dingbat incision, which is an incision along the midline, anteriorly to the hairline, posteriorly to the external occipital ridge, and then from the zygomatic arch to the midpoint of the midline, which has the advantage of better preservation of the flap blood supply and faster recovery. The bone flap is removed free, the dura is cut, and intraoperative cortical EEG monitoring is performed at all sites. The middle cerebral artery is separated by opening the lateral fissure and cut at its bifurcation (i.e., above the doublestem artery and the penetrating artery), and then the paramedian reflux vein as well as the inferior temporal reflux vein are cut sequentially along the sagittal sinus. The hemisphere is lifted along the falx and separated to the corpus callosum, where the pericallosal artery is visible, and the anterior cerebral artery is cut by probing to the lower part of the anterior knee of the corpus callosum. The corpus callosum is dissected to expose the affected ventricle, and the hemisphere is dissected and separated along the ventricle. The insular cortex, temporal lobe, amygdala, and hippocampus are also dissected together, preserving the basal ganglia and thalamus. The residual choroid plexus in the ventricle is excised, the interventricular foramen is sealed with a small piece of muscle tissue, and the dura is sutured and fixed at the base of the falx, cerebellar curtain, anterior, and middle cranial fossa, making the residual cavity an epidural cavity. Functional hemispherectomy, pioneered by Rasmussen in 1974, refers to a functionally complete, anatomically incomplete hemispherectomy in which only the central region and temporal lobes and hippocampus are removed, the corpus callosum is completely dissected, and the prefrontal and posterior parieto-occipital lobes are severed from brainstem connections and preserved in isolation. The procedure has also undergone continuous improvement, especially the functional hemispherectomy via the lateral fissure, which started after 1992, all with the main aim of shortening the operative time and reducing trauma and complications. Common postoperative complications include infection, hemorrhage, and, in the late stage, hydrocephalus and iron-containing heme deposits on the brain surface. In recent years, due to continuous improvement of surgical protocols, late complications have become rare. Early postoperative fever is more common in younger children, and symptomatic management is usually sufficient. The Johns Hopkins Children’s Center in the United States studied 106 hemispherectomies from 1975 to 2001 and reported that the fever that follows hemispherectomy is usually harmless. Because of this, most of these children may not require spinal puncture or other aggressive treatment.