Undetermined predominant polarity in a cohort of bipolar disorder patients: Prevalent, severe, and overlooked

•In bipolar disorder (BD) having a clear depressive or manic predominant polarity (PP) may guide clinical choices, but the majority of patients with BD do not show a clear PP•A cross sectional study on 708 patients with bipolar disorders recruited from a specialized center to explore clinical correlates of undetermined predominant polarity (UPP)•UPP was identified in 437 patients (61.7%) and was significantly associated with a higher number of relapses, aggressive behaviour and a seasonal pattern of illness.•UPP represent an overlooked subpopulation of BD with worse clinical outcomes compared to depressive or manic PP Predominant polarity (PP) is a concept used to define patients with bipolar disorder (BD) as presenting a tendency to manifest depressive (DPP) or manic (MPP) episodes. Still, the high percentage of patients with an undetermined PP (UPP), has been overlooked in most studies. Thus, we aimed to study UPP and outline its socio-demographic, clinical, and treatment-related features. Patients were recruited from a BD specialized unit. The sample was divided into three groups according to PP and socio‐demographic and clinical variables were compared. Significant variables at univariate comparisons were included in multivariate logistic regression with UPP as the dependent variable. A total of 708 BD patients were included, of which 437 with UPP (61.7%). UPP was associated with a higher number of affective relapses, when compared with DPP or MPP (χ2= 28.704, p