The ketogenic diet has been used in the treatment of intractable childhood epilepsy since the 1920s. A systematic review of the efficacy, adverse reactions, and costs associated with using the diet was performed. PubMed and Ovid searches were performed using the keywords epilepsy/therapy, dietary therapy, ketogenic diet, adverse events, and costs. Cochrane library was searched. Bibliographies of papers located by searches and review articles were compiled. Papers published after 1990 were selected if they were written in either English or French and reported on the use of classic ketogenic diet in patients under age 18 years of age with medically refractory epilepsy. Outcome measures were degree of seizure control, duration patient remained on diet, and occurrence of adverse events. Twenty-six studies were found. No prospective-controlled studies were found. Fourteen studies met all criteria for inclusion. The studies indicated that some children report reduction in seizure frequency. The estimated rate for obtaining complete seizure control was 15.6% (95% confidence interval 10.4-20.8%) with 33% (95% confidence interval 24.3-41.8%) reporting greater than 50% reduction in seizures. Adverse events were not frequent; however, 16 cases of death occurring while on the diet were found. No cost/benefit studies were located. There is evidence to support the cautious use of ketogenic diet in children with refractory epilepsy.