A case of a 14-year-old girl suffering from intense headaches is presented. At the first pediatrician's examination, the patient had regular findings. Prolonged P100 wave latencies were found by testing the visual evoked potentials. After further examination following repeated headaches, Arnold Chiari type I malformation was diagnosed. Arnold Chiari malformation is classified as downward displacement of one or both cerebellar tonsils through foramen magnum. The most common symptom is occipital or suboccipital headaches that usually happens after hard physical effort. Changes in visual evoked potential latencies can be present before other clinical symptoms and can be a useful tool in the diagnostics of headaches in children and adolescents.