The high fat, low carbohydrate, low protein ketogenic diet (KD) has been used to control refractory epilepsy in children since 1920, although its mechanism of action is unknown. Previous animal studies have shown that the KD can increase acute seizure threshold, but the effect of the KD on the process of epileptogenesis has not been studied. We tested the effect of an experimental KD on epileptogenesis in adult rats using the kainic acid (KA) model. P54 rats underwent KA-induced status epilepticus, followed by assignment to a control diet or a KD consisting of (by weight), 14% protein, 70% fat and no carbohydrate. KD-fed animals tolerated the diet and maintained ketosis. KD-fed rats had significantly fewer and briefer spontaneous recurrent seizures and less supragranular mossy fiber sprouting, although the degree of hippocampal pyramidal cell damage was similar in both groups. These results provide the first evidence that the KD retards epileptogenesis in an experimental model.