Ketogenic diet (KD) was usually tried as a last resort in the treatment of intractable epilepsy after failure of many antiepileptics and even epilepsy surgery. Glucose transporter-1 deficiency and pyruvate dehydrogenase deficiency must be treated with KD as the first choice because of inborn errors of glucose metabolism. Infantile spasms, tuberous sclerosis complex, Rett syndrome, Doose syndrome, Dravet syndrome, etc., appear to respond to KD, and it has been suggested by the international consensus statement to use KD early. We believe that all patients with epilepsy, except those with contraindicated situations such as pyruvate carboxylase deficiency, porphyria, β-oxidation defects, primary carnitine deficiency, etc., may try KD before trying other regimens.