BackgroundRapid-cycling (RC; ≥ 4 episodes/year) in bipolar disorder (BD) has been recognized since the 1970s and associated with inferior treatment response. However, associations of single years of RC with overall cycling rate, long-term morbidity, and diagnostic subtypes are not clear.ResultsWe compared descriptive and clinical characteristics in 1261 BD patients with/without RC, based on history and prospective follow-up for several years. RC in any previous year was identified in 9.36% of BD subjects (3.74% in BD1, 15.2% BD2), and somewhat more among women than men. RC-BD subjects had 3.21-fold greater average prospective annual rates of recurrence but not hospitalizations, had less difference in %-time-ill, received more mood-stabilizing treatments, and had greater suicidal risk, lacked familial psychiatric illnesses, had more cyclothymic temperament, were more likely to be married, had more siblings and children, experienced early sexual abuse, but werelesslikely to abuse drugs (not alcohol) or smoke. In multivariable regression modeling, older age, mood-switching with antidepressants, and BD2 > BD1 diagnosis, as well as more episodes/year were independently associated with RC. Notably, prospective mean recurrence rates werebelow4/year in 79.5% of previously RC patients, and below 2/year in 48.1%.ConclusionsLifetime risk of RC in BD was 9.36%, more likely in women, with older age, and in BD2 > BD1. With RC, recurrence rates were much higher, especially for depression with less effect on %-time ill, suggesting shorter episodes. Variable associations with unfavorable outcomes and prospective recurrence rates well below 4/year in most previously RC patients indicate that RC was not a sustained characteristic and probably was associated with use of antidepressants.