Nonmotor functions of the cerebellum are well known. Within this frame, the aim of this study was to compare psychiatric morbidity rates among patients affected by cerebellar diseases or Parkinson's disease (PD). Forty-seven patients (27 cerebellar and 20 PD) underwent a comprehensive psychiatric evaluation (psychopathological rating scales and the Structured Clinical Interview for DSM-IV-TR Axis I Disorders). Psychiatric disorders were slightly more frequent among cerebellar than among PD patients (89% vs. 75%; p = 0.21). Mood disorders were more frequent in the cerebellar than in the PD group (90% vs. 55%; p < 0.01). Among those subjects with no psychiatric history prior to the onset of neurological disease, bipolar spectrum disorders were more frequent within the cerebellar group (p < 0.01). These results confirm high rates of psychiatric disorders among cerebellar patients. The higher frequency of bipolar spectrum presentations found in the cerebellar group may suggest a specific involvement of cortico-cerebellar circuits in the pathophysiology of mood dysregulation.