During the last two and one-half years, the ketogenic, or high fat, diet has been given a trial in the treatment of epilepsy in childhood. Thirty-seven patients with essential or idiopathic epilepsy, whose parents were able to comprehend and carry out the diet intelligently at home, have been observed over periods of from four months to two and one-half years. Twenty of the patients were boys and seventeen girls. Their ages ranged from 2¼ to 14½ years, the median average age being 86/10 years. Seven of the patients had grand mal convulsions, seventeen petit mal, and thirteen both grand and petit mal. Not one with obvious organic disease of the central nervous system or with any other evidence of mental deterioration was included in this series. There were hereditary taints in nineteen cases, migraine or sick headache in ten, epilepsy in three, "nervousness" in three, and syphilis in three. In