Few case reports discuss suspected psychiatric disturbances secondary to arachnoid cysts. To the best of our knowledge, psychosis from arachnoid cysts has not been reported in the recent literature. This case report discusses our experience with a 55-year-old male patient who manifested multiple psychotic episodes suspected in association with an arachnoid cyst. During the initial examinations, a computed tomography (CT) scan of his head revealed a relatively large left anterior superior arachnoid cyst with a mass effect on the frontal lobe. Despite multiple trials of combinations of mood stabilizers and psychotropic medications, the patient continued to deteriorate. We ordered a repeat CT of his head along with a magnetic resonance image and consulted a neurosurgeon for a possible surgical intervention. The neurosurgeon concluded that the patient's psychiatric symptoms were unrelated to the arachnoid cyst. While we were unable to determine the etiology of our patient's psychosis, we believe that the arachnoid cyst played at least some part, as evidenced by reports in the literature. Future advancements in radiological technology may allow for a better exploration of the causal relationship between psychiatric illnesses and brain lesions.