Borderline personality disorder (BPD) is a mental health condition characterized by unstable relationships, self-image, and emotions, as well as impulsive behaviors and high rates of morbidity and mortality. Provider-based stigmatization of individuals with BPD is associated with poor health outcomes and increased mortality risk. However, little is known about social workers' experiences in providing care to people living with BPD (PLBPD). This study explored social workers' perspectives on the impact of stigma on care for PLBPD. Between April 2020 and January 2021, qualitative semi-structured interviews were conducted with 41 social workers practicing across the continuum of care (e.g., community services and hospitals) in Ontario, Canada. Data were analyzed using Critical Realist Analysis. Four primary themes emerged: (1) stigmatization of PLBPD due to the complexity of their needs (e.g., avoidance, blame, name-calling by providers); (2) lack of BPD-specific training and education in social work curricula; (3) observed stigmatization of PLBPD by social workers and other professionals (e.g., psychologists and physicians); and (4) suggestions for improving care experiences for PLBPD. Results suggest that provider-based stigma remains a significant quality of care issue affecting PLBPD. Further research is needed to understand the scope of these issues among diverse PLBPD populations, within social work practice, and across interprofessional care settings.