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Arachnoid cysts have primary and secondary types. The prevalence of Arachnoid cysts is about 1% of all tumors in cranial cavity. Based on anatomic position, arachnoid cyst can cause different clinical manifestations including hemiparesis, increase intracranial pressure, macrocephaly and isolated headache and stop body growth. The natural course of the disease is not exactly clear. Some of patients have no symptoms during life and some of them may show some symptoms after a while. This case report is about a 10 years boy who had no sign except generalized headache. Anatomic position of the cyst was in right temporal lobe of the brain on the temporal, parietal and the great wing of sphenoid bones. Arachnoid cyst diagnosed through MRI and CT-Scan. Patient treated with ibuprofen for three days and then patient followed up to treat with surgery method when other clinical symptoms appeare in the patient.