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The etiology of psychosis varies; it may be due to a functional or an organic condition. Psychosis in an organic basis can be caused by space occupying lesions in CNS, endocrine reasons, nutritional deficiencies, infections and substance and/or alcohol abuse and dependence. Arachnoid cysts are rare space occupying lesions formed by an arachnoid membrane containing cerebrospinal şuid. They are congenital, mostly asymptomatic and diagnosed accidentally by neuroimaging. Recently the coexistence of arachnoid cysts with psychosis has captured the popular attention about possible relevancy. In our case report, we present two patients with first episode psychosis who have never sought a psychiatric consult before. Case 1 is a 36 years old male who presented with delusions of persecution and reference about his family and resulting aggressiveness towards them. In magnetic resonance imaging of his central nervous system, there was an arachnoid cyst in anterior pole of right temporal lobe about 2.5x4.5 cm in size. Case 2 is a 52 years old male who presented with intense delusion of jealousy about his wife. In magnetic resonance imaging of his central nervous system, the was an arachnoid cyst in the posterior of the midline of the posterior cranial fossa about 3x4.5 cm in size. Both cases revealed no pathologic neurological signs. The MRI of the both cases are consulted with neurosurgery, no surgical intervention was needed. In this study, we discuss the treatment to these cases and the relevancy of arachnoid cysts with first episode psychosis.