Background: Social deficits and emotional dysregulation have been suggested as explanations for the relational difficulties experienced by patients with borderline personality disorder (BPD). The neuropeptide oxytocin (OXT) is a possible neurobiological underpinning of these adversities, and this study examines possible correlations between BPD symptomatology and serum OXT. Methods: Thirty-eight female participants (BPD group n = 18, matched control group n = 20) with a mean age of 29.5 years (standard deviation 9.2) were assessed for personality disorders, general psychopathology, childhood trauma and perceived stress. OXT was measured in serum samples. Results: We found no significant difference between patient and control group in terms of OXT levels. However, post hoc analysis showed a relationship in the patient group between civil status and OXT (p < 0.05), indicating higher levels of OXT for patients in a romantic relationship. Discussion: The idea of OXT as a pro-social love hormone is perhaps too simplistic, and factors like attachment style, exposure to trauma and psychiatric disorders must be considered in order to understand its diverse functions. Conclusions: Contrary to our expectations, we did not find lower serum OXT levels in the BPD group. However, BPD patients in a romantic relationship had higher levels of serum OXT than single BPD patients.