In 1921, the classic ketogenic diet was created at the Mayo Clinic in Rochester, Minnesota to treat epilepsy in children and adults. Over a century later, it is a widely used, standard-of-care therapy for typically treatment-resistant epilepsy worldwide. There are currently five versions of ketogenic diet therapy that can be started either in or out of the hospital setting. It is overall effective in approximately half of children started, usually within a few months. Established indications for ketogenic diet therapy exist, in which this treatment may potentially even be more advantageous than antiseizure medications. Some of these indications include Glut1 deficiency, pyruvate dehydrogenase deficiency, infantile epileptic spasms syndrome, epilepsy with myoclonic-atonic seizures, and formula-fed children. Although most children are also receiving antiseizure medications with ketogenic diet therapy, its use may lead to medication reduction or withdrawal in some cases, and improvement in cognition and quality of life. Supplements are begun when ketogenic diet therapy is initiated in order to prevent common side effects, including constipation, kidney stones, growth disturbance, and dyslipidemia. Typically, after 2 years in most children, ketogenic diet therapy is discontinued gradually.