The purpose of this study was to determine time of onset of ketosis and efficacy when the classic ketogenic diet is initiated at full calories without a prior fast in children with epilepsy. A retrospective hospital and neurology clinic chart review was done of all 14 children commenced on the classic ketogenic diet at full calories without a prior fast between January 1, 1997, and May 31, 2001, to determine time to ketosis, time to good ketosis (urine ketones > or =80 mg/dL), and success of the ketogenic diet. Median age at diet initiation was 63 months (25th-75th percentile 47-149 months). There were 7 girls and 7 boys. Four had symptomatic generalized epilepsy, whereas the remainder had partial seizures +/- secondary generalization. Twelve of 14 children suffered seizures on a daily basis prior to the ketogenic diet. Six were commenced on the diet as outpatients, whereas 8 were admitted to hospital. No patients were fasted. All admitted patients were started on a 1:1 ketogenic ratio at full calories for the first 24 hours and advanced to a 3:1 or 4:1 ratio over 3 to 4 days, while outpatients were started on a 1:1 or 2:1 ratio and similarly advanced. Thirteen of 14 patients were successfully started on the diet, with 1 developing vomiting and food refusal during the initial hospitalization but after ketosis was established. One child was lost to follow-up after initial hospital discharge. Information regarding time to ketosis was determined for all inpatients. Mean time to onset of ketosis was 33 hours (range 17 to 48) and to good ketosis, 58 hours (range 40 to 84). Five of 12 children (42%) experienced success with the ketogenic diet, and all of these had their antiepileptic medications either withdrawn (n = 3) or decreased (n = 2). The ketogenic diet can be effectively initiated without a fast in children with epilepsy. Time to ketosis and diet efficacy are similar to protocols that use a fast.