A series of 33 (4.29%) cases of rapid cycling affective disorder (RCAD ICD-10-DCR) out of a pool of 770 consecutive cases of ICD-10 affective disorder (AD) was collected over a period of 5 years. All cases of RCAD belonged to bipolar affective disorder. RCAD when compared with non-rapid cycling bipolar affective disorder (BPAD) revealed a significantly longer mean duration of illness, greater number of total episodes, greater number of hospitalizations and stronger family loading of bipolar affective disorder. These findings implicate RCAD as a severe form of bipolar affective disorder.