Borderline Personality Disorder (BPD) is a common and severe mental illness that is infrequently included under state mental health parity statutes. This review considers BPD parity, using the Massachusetts mental health parity statute as a model. While BPD can co-occur with other disorders, studies of its heritability, diagnostic validity/reliability, and response to specific treatments indicate it is best considered an independent disorder, one that negatively impacts the patient's treatment response to comorbid disorders, particularly mood disorders. Persons with BPD are high utilizers of treatment, especially emergency departments and inpatient hospitalizations-the most expensive forms of psychiatric treatment. While some patients remain chronically symptomatic, the majority improve. The findings from psychopharmacologic and other biologic treatment data, coupled with associated brain functioning findings, indicate BPD is a biologically-based disorder. Clinical data indicate that accurately diagnosing and treating BPD conserves resources and improves outcomes. Based on this analysis, insuring BPD in the same manner as other serious mental illnesses is well-founded and recommended.