Mega cisterna magna (MCM) is a developmental malformation of the posterior fossa, morphologically vermis and cerebellar hemispheres are intact. Although the relationship between this anomaly and psychiatric disorders is emphasized, its nature has not fully understood. In this article, we report a case of schizophrenia detected mega cisterna magna. A 35-year-old, married, housewife, graduated from primary school, female patient was brought to our clinic by her relatives with complaints of disorganized and inappropriate speech, strange behavior. She had auditory and visual hallucinations, delusions of reference and persecution. Neurological examination and EEG examination were normal, but mega cisterna magna was disclosed in her cranial magnetic resonance imaging scan. The relationship between psychosis and clinical significance of MCM has not defined completely yet. The role of the cerebellum in schizophrenia has been highlighted by Andreasen s hypothesis of cognitive dysmetria . This hypothesis suggests that cerebellum has a role in general dyscoordination of sensorimotor and mental processes which are seen in schizophrenic patients. Schizophrenic patients are known to have problems about memory and verbal fluency, too. In the context of this case, the relationship of schizophrenia with cerebellar anomalies was reviewed.