Objective Individual differences in attachment insecurity are important in a broad range of mental health problems. However, few empirical studies have examined the clinical factors that contribute to individual differences in attachment style. This study examines the nature of interrelationships among adult attachment styles, sensitivities of behavioral activation system/behavioral inhibition system (BIS/BAS), and childhood trauma in patients with depressive disorders. Methods Patients with depressive disorders (n=294) completed self-report questionnaires evaluating adult attachment style, childhood trauma, and BIS/BAS sensitivity. We performed multiple regression analyses to examine the associations between attachment style and other clinical factors, including childhood trauma and BIS/BAS sensitivity. We also conducted hierarchical regression analyses and simple slope analyses to examine the interaction between BIS/BAS sensitivity and childhood trauma. Results The BAS sensitivity was negatively associated with attachment avoidance. The higher was the BIS/BAS sensitivity, the higher was the level of attachment anxiety. Among childhood trauma, emotional neglect contributed to both dimensions of insecure attachment. The interaction between BAS sensitivity and emotional neglect is significantly associated with attachment anxiety. Conclusion This study used data regarding the interrelationship of childhood trauma and basic motivational systems to contribute to the understanding of adult insecure attachment behaviors, a risk factor for depression.