Dandy-Walker malformation is defined by enlarged posterior fossa, cystic dilatation of the fourth ventricle, and cerebellar hypoplasia. Although developmental delay and mental retardation are common in Dandy-Walker malformation cases, other comorbid psychiatric conditions have been rarely reported. There are limited numbers of case reports about comorbidity of bipolar disorder with DandyWalker malformation in the literature. Herein, a Dandy-Walker malformation case presenting affective symptoms is reported, and psychiatric symptoms which might be seen in this rare malformation are discussed along with diagnosis, treatment, and follow-up processes. A 27-year-old male patient, hospitalized for compulsory treatment, had been diagnosed with Dandy-Walker malformation in childhood. First complaints were attention deficiency, behavioral problems, learning difficulties; and manic and depressive episodes have occurred during follow-ups. He recently complained of decreased need for sleep, irritability, and increased speed of thought, and psychiatric examination was consistent with manic episode. Cranial computed tomography (CT) revealed bilateral ventriculomegaly, enlarged third and fourth ventricles with posterior fossa cyst, and cerebellar hypoplasia. His treatment included 30 mg/day aripiprazole, 1000 mg/day valproic acid, 200 mg/day quetiapine, 4 mg/day biperiden, and 100 mg/month paliperidone palmitate. Beside its traditional role in the regulation of coordination and motor functions, cerebellum is increasingly emphasized for its involvement in the mood regulation. Thus, as seen in Dandy-Walker malformation, cerebellar anomalies are suggested to play a role in the pathophysiology of mood disorders. Further studies are needed to better understand the relationship between mood disorders and cerebellum. Moreover, treatment options should be considered carefully in terms of resistance to treatment and potential side effects, for psychiatric disorders occurring in these cases; and detailed examinations, including cranial imaging, would be beneficial in bipolar cases with early onset, unresponsiveness to treatment, presenting atypical symptoms, mental retardation, and developmental delay as well as neurological symptoms and signs.