Patients and families with arachnoid cysts combined with epilepsy often believe that this cyst is the cause of the seizures and that curing this cyst will eradicate the seizures. Because the arachnoid cyst is often the patient’s only abnormal finding, and according to general medical rules, many physicians will also hold this view. However, many clinical data from the last 10 years or so show that the epileptic focus happens to be located adjacent to the cyst in less than 20% of these patients. in more than 80% of patients, the epileptic focus is far from the cyst. For example, in patients with temporal lobe arachnoid cysts, the epileptic focus is located in the frontal or parietal lobe, or even in the contralateral hemisphere. In these patients, treatment of the cyst alone is clearly not effective in controlling the seizures, and it is necessary to find and remove the epileptic focus that is distant from the site. The cause of arachnoid cysts is not fully understood. Although there are several theories, none of them can fully explain many clinical phenomena. Therefore, there is no accepted explanation for the above-mentioned phenomena that seem to defy general medical rules.