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Background: The concept of predominant polarity (PP) is defined as presenting more symptoms of one polarity. Previous studies have defined PP as one polarity (either a depression or mania episode) occurring during at least two-thirds of the lifetime., Methods: We conducted an observational study with the COPE-BD (Clinical Outcome and Psycho-Education for Bipolar Disorder, Clinical Outcome Measures Section) dataset to identify the diagnostic and treatment differences between bipolar disorder (BD) patients with and without PP., Results: The final sample included 210 BD-I (59.0%) and 146 BD-II (41.0%) patients. Of these, 28.9% patients presented predominant polarity (PP): 62 (17.4%) of those patients were depressed polarity predominant (DPP), 41 (11.5%) were manic polarity predominant (MPP), and 253 (71.1%) met criteria for bipolar disorders but did not present with PP. In comparison to this group of BD patients with undetermined polarity, the group of BD patients with PP presented more rapid cycling. Furthermore, in the undetermined polarity group, the onset of illness occurred earlier, and the duration of the illness was longer, with more hypomanic/manic and depressive episodes than patients who met the PP criteria., Limitations: This study has a naturalistic and retrospective design and does not allow a specific follow-up of polarity over time., Conclusions: These different clinical characteristics underline the importance of considering PP in patients with BD, and justify the need for differential treatment approach which could have an impact on patients' prognosis. Yet, more independent and prospective research is needed to confirm these findings, especially with the new classification of DSM-5 concerning mixed states., (Copyright © 2019. Published by Elsevier B.V.)