Introduction. The deficit of the type 1 glucose transporter (Glut1-DS) belongs to the neurometabolic disorders that can be effectively treated, in this case with ketogenic diet. By limiting glucose supply to the brain the deficit of glucose transporter 1 leads to cerebral energy deficiency. Glut1-DS manifests with a wide range of neurological symptoms that usually start in early childhood, including cognitive impairment, epilepsy and permanent and/or paroxysmal motor disorders, often provoked by physical activity, fasting or hyperthermale. Aim. We present the case of a 6,5-year-old patient with Glut1- -DS who, despite presenting typical symptoms, remained undiagnosed for years. Family history was positive of intellectual disability in first degree relative. The child suffered from psychomotor development delay, motor coordination difficulties, motor disorders and epilepsy with focal and absence seizures of early onset. However, the significant symptom of secondary microcephaly remained unnoticed for years. Conclusion. Secondary microcephaly is a valuable symptom which can guide towards the diagnosis. The early diagnosis of Glut1 deficiency syndrome enables prompt introduction of the ketogenic diet crucial for the child’s development and improvement of both the patients and their families’ quality of life.