Borderline personality disorder (BPD), which is characterized by unstable moods, behavior, and relationships, is also associated with heightened suicidal ideation. Prior research has demonstrated that BPD and suicidal ideation are prevalent among women in substance use treatment. Efforts to treat substance use in this population are made difficult due to the severity of BPD, and it is possible that mindfulness-based interventions specific to substance use could be an effective approach for this population. However, basic research is needed on the relationship between dispositional mindfulness, BPD, and suicidal ideation among women in treatment for substance use to support their associations, which was the purpose of the present study. Pre-existing medical records were reviewed from a residential substance use treatment center. A total of 81 female patients were included in the current study. Patients completed self-report measures of mindfulness, BPD, suicidal ideation, substance use, and impression management at treatment intake. Findings demonstrated dispositional mindfulness to be negatively associated with BPD features and suicidal ideation. With the exception of self-harm, this negative relationship was found even after controlling for age, substance use, and impression management. Future research should examine whether mindfulness-based interventions are an effective treatment for comorbid substance use and BPD.