Since its introduction in 1921, the ketogenic diet has been in continuous use for children with difficult-to-control epilepsy. After decades of relative disuse, it is now both extremely popular and well studied, with approximately two-thirds of children demonstrating significant seizure reduction after 6 months. It is being used for less intractable seizures in children as well as recently adults. Modifications that help improve tolerability include the medium chain triglyceride diet, modified Atkins diet, and low glycemic index treatment. Major side effects include acidosis, increased cholesterol, kidney stones, gastroesophageal reflux, and growth disturbance. However, these side effects are usually treatable and nowadays often even preventable. Future non-epilepsy indications such as Alzheimer disease, amyotrophic lateral sclerosis, autism, and brain tumors are under active investigation. This dietary treatment for epilepsy has undergone a rebirth. Its widespread use in Poland and Europe is a welcome additional treatment for those with drug-resistant epilepsy.