Bipolar disorder is a mood (affective) disorder characterized by the occurrence of alternating feelings of excitement (mania) and depression. It is a common, but serious condition, and potentially life-threatening. Patients are considered to have a rapid cycling form of bipolar disorder if they experience four or more episodes of hypomania (mild degree of mania), mania, and/or depression. Approximately 20% of the patients in bipolar clinics have the rapid cycling form of the disorder. Therefore it can be said that RCBD is not a rare condition and that it can severely impair a patient. These reasons alone justify studying RCBD. However, researchers also believe that information gathered by studying patients with RCBD can be used while studying other patients with different forms of bipolar disorder.