• bipolar I disorder;
  • bipolar II disorder;
  • course of illness

Objectives:  To assess the proportion of time spent in mania, depression and euthymia in a large cohort of bipolar subjects studied longitudinally, and to investigate depression/mania ratios in patients with bipolar I versus bipolar II disorder.

Methods:  Clinician-adjusted self-ratings of mood were completed daily for one year for naturalistically treated outpatients with bipolar I (n = 405) or bipolar II (n = 102) disorder. Ratings were analyzed for mean time spent euthymic, depressed, manic, hypomanic, and cycling, and the percentages of time spent ill were compared between the two groups.

Results:  Percentages of time spent ill for bipolar I versus II patients were: euthymia 47.7% versus 50.2%; depression 36.0% versus 37.0%; hypomania 11.5% versus 9.8%; mania 1.0% versus 0.2%; and cycling 3.7% versus 2.8%. The depression/mania ratio was 2.9 in the bipolar I and 3.8 in bipolar II sub-groups.

Conclusions:  Depression represents the predominant abnormal mood state for treated outpatients with bipolar I and II disorder. In contrast to other studies, we found that depression/mania ratios were of a similar magnitude, suggesting the same tendency towards mood instability in both sub-groups.