This chapter provides a summary of a landmark study on borderline personality disorder. What is the long-term prognosis of those with borderline personality disorder (BPD) compared to those with major depressive disorder or other personality disorders? Starting with that question, it describes the basics of the study, including funding, study location, who was studied, how many patients, study design, study intervention, follow-up, endpoints, results, and criticism and limitations. The findings show a favorable long-term prognosis that is comparable to that of other psychiatric disorders; 85% of those with BPS show at least 12-months of continuous remission after ten years. The chapter briefly reviews other relevant studies and information, discusses implications, and concludes with a relevant clinical case.