Abstract
Background: Psychiatric disorders can be caused by organic conditions. Arachnoid cysts are suggested to be related to psychiatric disorders since many case reports have be published presenting coexistence of arachnoid cyst and psychosis.

Case report: An 18-year-old single male was admitted to the psychiatry hospital with severe fearfulness, disorganized behavior, decreased sleep, and refusal of oral intake. He had delusions of guilt, persecution and misidentification. He also showed periods of incoherent and very poor speech, perplexity, disorientation, and some catatonic features. There was no history of substance use or significant medical problem. Physical, including neurological, examination and laboratory investigations were normal. A brain CT revealed the presence of an arachnoid cyst in the left temporal lobe. He was treated pharmacologically with partial and slow response.

Conclusion: Causal relationship between arachnoid cyst and psychosis is difficult to be concluded in this case, but the possibility should not be ignored. This case is reported from Arab region where there is lack of such publications. More in-depth research is needed.

Key words: Psychosis; Temporal lobe; Arachnoid Cyst; Arab; Case report