We present the experience of using the ketogenic diet (KD) in the treatment of pharmacoresistant epilepsy in a patient with glucose transporter deficiency syndrome type I (GLUT1). We observed a nine-year-old boy with refractory epilepsy with frequent multiple myoclonic seizures due to GLUT1. The high effectiveness of KD in the treatment of GLUT1 was demonstrated. By the 10th day from the beginning of KD, a complete relief of epileptic seizures and EEG abnormalities was achieved. After 3 months, we noticed positive signs in cognitive and speech development of the child. Antiepileptic drugs were withdrawn due to the stable remission. Subsequently there was a further positive dynamics in intelligence, psycho-emotional sphere; the child began attending a special school. By this time the patient continued the diet for 1 year and 3 months. A significant improvement in the patient’s condition is maintained, observation is being continued. In conclusion, the ketogenic diet seems to be a highly effective and, perhaps, exclusive method for GLUT1 treatment.