BACKGROUND Research is increasingly focusing on identifying factors distinguishing patients who complete vs. dropout of residential substance abuse treatment. One potentially relevant factor that has received relatively little attention is borderline personality disorder (BPD). METHODS This study sought to examine the effect of BPD on residential substance abuse treatment dropout within a sample of 159 male patients with substance use disorders-a population often understudied with regard to BPD and at high-risk for treatment dropout. Patients were administered a structured diagnostic interview to establish BPD diagnoses. Patients were then followed throughout the course of residential substance abuse treatment to identify those who completed treatment and those who prematurely dropped out of treatment. RESULTS Patients with BPD were significantly more likely to prematurely dropout of treatment, and this finding remained even when taking into account relevant covariates (i.e., court-ordered treatment status, contract duration, and major depressive disorder). Further, patients with BPD were more likely to experience center-initiated dropout as opposed to voluntary withdrawal from treatment. CONCLUSIONS These findings add to the literature on BPD-SUD co-occurrence, suggesting that the presence of co-occurring BPD among male SUD patients may increase the risk for dropout from residential substance abuse treatment, necessitating targeted interventions focused on decreasing dropout within this patient subgroup.