OBJECTIVE: To evaluate aggressiveness during a major depressive episode (MDE) and its relationship with bipolar disorder (BD) in a post hoc analysis of the BRIDGE-II-MIX study. METHOD: A total of 2811 individuals were enrolled in this multicenter cross-sectional study. MDE patients with (MDE-A, n = 399) and without aggressiveness (MDE-N, n = 2412) were compared through chi-square test or Student's t-test. A stepwise backward logistic regression model was performed. RESULTS: MDE-A group was more frequently associated with BD (P < 0.001), while aggressiveness was negatively correlated with unipolar depression (P < 0.001). At the logistic regression, aggressiveness was associated with the age at first depressive episode (P < 0.001); the severity of mania (P = 0.03); the diagnosis of BD (P = 0.001); comorbid borderline personality disorder (BPD) (P < 0.001) but not substance abuse (P = 0.63); no current psychiatric treatment (P < 0.001); psychotic symptoms (P = 0.007); the marked social/occupational impairment (P = 0.002). The variable most significantly associated with aggressiveness was the presence of DSM-5 mixed features (P < 0.001, OR = 3.815). After the exclusion of BPD, the variable of lifetime suicide attempts became significant (P = 0.013, OR = 1.405). CONCLUSION: Aggressiveness seems to be significantly associated with bipolar spectrum disorders, independently from BPD and substance abuse. Aggressiveness should be considered as a diagnostic criterion for the mixed features specifier and a target of tailored treatment strategy.