Little is known about comorbidities of bipolar disorder such as Parkinson's disease. A case history and a literature survey indicate that bipolar disorder is linked with or influences Parkinson's disease and vice versa. Underlying mechanisms are poorly understood, and, more importantly, no treatment options are established in such double diagnoses. The few data in comorbid Parkinson cases seem to point to a rapid cycling pattern of bipolar symptoms. With regard to therapeutic intervention, the literature supports pramipexole for treatment of both Parkinson and depressive symptoms in bipolar depression. Lithium, the mood stabilizer of choice for treating manic states, is problematical for use in Parkinson patients because of its side effects. Valproate might be an alternative, especially for treatment of rapid cycling.