Glucose transporter-1 deficiency syndrome (GLUT1-DS) is caused by a decreased function of the glucose transporter GLUT1 protein, which is located in the blood brain barrier. This leads to inadequate glucose levels for brain metabolism and can cause various clinical symptoms including medically intractable epilepsy, developmental delay and complex movement disorders. Ketonic diet is the golden standard for treatment of GLUT1-DS. GLUT1-DS should be suspected in patients with early-onset intractable epilepsy with developmental delay or activity-induced movement disorders with or without epilepsy.