Concomitant substance misuse in adults with borderline personality disorder (BPD) is associated with a more severe course of illness and poorer outcomes. Previous research has found an association between the number of borderline personality features and substance misuse in community samples. This study examined the relationship between substance use and severity of BPD in youth presenting for the first time for treatment (first presentation) of BPD. Participants were 117 help-seeking youth aged 15–25 years (93 females; Mage = 19.0 years, SD = 2.8) with BPD. Hierarchical logistic regression was used to investigate whether the severity of BPD predicted substance use. After adjusting for demographic factors and concurrent mental state pathology, BPD independently predicted alcohol dependence, amphetamine use in the previous month, or use of 2 or more illicit substances in the previous month but not daily tobacco use or cannabis use in the previous month. BPD might increase the probability that an individual will engage in higher-risk behaviors, such as amphetamine and polysubstance use, or problematic alcohol use. These findings support the need for assessment of youth with BPD for alcohol, amphetamine, and polysubstance use along with the need for routine screening in drug and alcohol services for BPD features.