Here we report the case of a patient with psychotic symptoms apparently resistant to antipsychotic treatments. Since the last admission in a psychiatric division the patient was diagnosed with Bipolar Disorder type I and then referred to our Outpatients Unit of Treatment Resistant Psychosis, where she was subsequently re-diagnosed with Dandy-Walker Syndrome. The Dandy Walker Complex is a congenital brain malformation involving the fourth ventricle and the cerebellum. We investigated the cognitive impairment of the patient and found deficits prominently in executive functions. This report may add further evidence on the importance of a correct diagnosis prior to defining a patient as treatment resistant and highlights cerebellar dysfunctions that may contribute to neuropsychiatric symptoms and cognitive impairment.