Most reports of the ketogenic diet have focused on its efficacy for generalized seizures. Few data are available regarding its effect on focal seizures. We retrospectively studied patients (mean = 7.5 years of age) with medically intractable epilepsy treated by the ketogenic diet. The predominant seizure types in each patient were classified as generalized (100 patients) or focal (34 patients) based on ictal electroencephalograms (EEGs) or seizure semiology and interictal EEG. A seizure reduction of more than 50% compared with baseline was seen in nine patients (27%) with focal seizures and 46 patients (46%) with generalized seizures at 3 months, in 10 patients (30%) with focal seizures and 46 patients (46%) with generalized seizures at 6 months, and in eight patients (24%) with focal seizures and 42 patients (42%) with generalized seizures at 12 months. Differences were not significant. Outcome tended to be better in patients younger than 12 years of age compared with the older age group, but the difference was significant at 6 months only. Our results suggest that some patients with intractable focal epilepsy may respond favorably to the ketogenic diet and that this option should be considered if epilepsy surgery is not possible.