Reports of volumetric abnormalities in the anterior cingulate cortex (ACC) in adults with established borderline personality disorder (BPD) are inconsistent, and it is not known whether such abnormalities are present early in the disorder. We aimed to investigate ACC volume in a first-presentation teenage BPD sample with minimal exposure to treatment. Fifteen female BPD patients and 15 healthy female control participants underwent magnetic resonance imaging (MRI) scanning. ACC volumes were estimated using a reliable method that accounts for inter-individual variation in sulcal morphology, and measurements were compared between the two groups. Analysis of variance revealed a decrease in volume of the left ACC in BPD patients compared with control participants. This volumetric change was correlated with parasuicidal behavior and impulsivity. A measure of ACC volume asymmetry was also correlated with fear of abandonment symptoms. Our results suggest that ACC volumetric abnormalities early in the course of BPD might be related to clinical correlates of the disorder. Longitudinal studies are needed to examine the nature of this abnormality over the course of the disorder.