Background: Previous research has linked insecure attachment styles and borderline personality organization to Substance Use Disorder (SUD). However, it still remains unclear whether those impairments apply to different kinds of SUDs to the same extent. Therefore, in this study we sought to investigate potential differences regarding attachment deficits and borderline personality organization in two different SUD inpatient groups, and furthermore in comparison to healthy controls. Sampling and Methods: 66 (24 female) inpatients diagnosed for Alcohol Use Disorder (AUD), 57 (10 female) inpatients diagnosed for Polydrug Use Disorder (PUD) and 114 (51 female) healthy controls completed the Borderline Personality Inventory and the Attachment Style Questionnaire. Results: Compared to healthy controls, AUD and PUD inpatients showed significant deficits in all attachment parameters (p<.01) as well as a significantly increased amount of borderline personality organization (p<.01). However, no differences between AUD and PUD inpatients were observed (p>.05). Conclusions: Our results indicate that the drug(s) of choice cannot be regarded as an indicator for the extent of attachment deficits or personality pathology. These initial findings are mainly limited by the rather small sample size as well as just a single-point of measurement. Future research might also consider further covariates such as comorbidity or psychotropic medication.