Objective The aims of current study were to determine whether childhood maltreatment contributes to the occurrence of major depressive disorder (MDD) with bipolarity or suicidality. Methods In total, 132 outpatients diagnosed with MDD between 2014 and 2015 on the medical records were included. The subjects were divided into two groups according to the presence of childhood maltreatment (CM group) and no childhood maltreatment (NCM group). Depression severity and bipolarity were identified using Beck Depression Inventory (BDI) and the Korean version of Mood Disorder Questionnaire (K-MDQ) respectively on the medical records. In addition, the baseline loud dependence of auditory evoked potentials of 36 patients on medical records Were analyzed. Results The mean total BDI, BDI item 9 (suicide ideation), and total K-MDQ score were significantly higher in the CM group than the NCM group. The number of subjects with bipolarity was significantly higher in the CM than in the NCM group. Furthermore two thirds subjects experienced the significant maltreatment during childhood. The central serotonergic activity of the CM group was also lower than that of the NCM group. Conclusion The findings of this study support that there is a relationship between childhood maltreatment and bipolarity or suicidality in patients with MDD.