A subtype of rapid cycling bipolar affective illness (RC) is presented from an aspect of its clinical appearances pathogenesis and treatment. RC was defined in 1974 and will be included in DSM-IV. Patients with RC (4 or more episodes per year) make up about 13% of all subjects with bipolar affective illness. The majority of them are females and nearly half of RC patients have family history of affective illness. In 1/3 of patients, the illness begins with RC in young age, in the remaining this is preceded by several years of "normal" course. The induction of RC may be related to the administration of antidepressant drugs, mostly tricyclics; in some patients, such course may remit upon discontinuation or change of such drugs. The inducing factor may be organic brain impairment and also stressful events operating by means of the "kindling" mechanism. Other pathogenetic concepts of RC point to a role of thyroid pathology and disturbances of circadian and circannual rhythms. Variability of the course and dynamics of RC may be conceptualized within the framework of chaos theory. The best therapeutic results in RC are obtained by combined treatment with two mood stabilizing drugs (e.g. lithium and carbamazepine, lithium and valproic acid) or by a combination of mood stabilizing drug with hypermetabolic doses of thyroxine.