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The cerebellum, which is known in general as an organ to control coordination, balance, and fine motor movements, has been demonstrated to have an important role in cognitive functions by using anatomical and functional imaging methods. The anomaly of mega cisterna magna is one of the various lesions of the posterior fossa which can inşuence cerebellar functions like cerebellar hypoplasia/agenesis, vermis hypoplasia/agenesis, Dandy-Walker malformation or variant, persistent Blake's pouch, arachnoid cyst, Joubert syndrome, and tumors of the posterior fossa. Mega cisterna magna (MCM) is a developmental malformation of the posterior fossa, where morphologically the vermis and cerebellar hemispheres are intact. Associated structural brain anomalies are common with mega cisterna magna and especially, MCM may be a component of the Dandy-Walker variant (with cerebellum hypoplasia) or Dandy-Walker syndrome (with cerebellum agenesia). Our knowledge about the relationship between this anomaly and psychiatric disorders is limited to very few case reports available. In this article, we report a case of schizophrenia associated with mega cisterna magna. A 35-year-old married patient (house wife, graduated from primary school) was brought to our clinic by her relatives with complaints of disorganized and inappropriate speech, strange behavior, and fear of people. She had auditory and visual hallucinations and delusions of reference and persecution. Up to five months ago she had no psychiatric or neurological symptoms or history. Her symptoms began with social isolation, decrease of self-care, and positive psychotic symptoms. Neurological examination and EEG examination were normal, but mega cisterna magna was discovered in her cranial magnetic resonance imaging scan. The patient was treated with risperidone 6mg/day for four weeks and was discharged after remission of psychotic symptoms. The prevalence and prognostic significance of MCM has not been defined completely yet. Memory and verbal şuency were found to be lower in cases of mega cisterna magna than in controls. Schizophrenic patients are known to have problems of memory and verbal şuency, too. The role of the cerebellum in schizophrenia has been highlighted by Andreasen's hypothesis of 'cognitive dysmetria'. This hypothesis suggests that the cerebellum has a role in the general dyscoordination of sensorimotor and mental processes which are seen in schizophrenic patients. The following observations demonstrating the involvement of the cerebellum are determined in studies of schizophrenic patients: high prevalence of neurological soft signs, dyscoordination, abnormal posture, balance problems, impaired eye blink conditioning and impaired adaptation of the vestibular-ocular reşex. Abnormal cerebellar activations have been showed in functional imaging studies. In the context of this case, the relationship of schizophrenia with cerebellar anomalies was reviewed.