This program was created to explain BPD in a way that is clear and easy to understand. Borderline Personality Disorder (BPD) is a complex, controversial and widely misunderstood mental illness. It’s been estimated that 1.6 % of adults in the United States struggle with BPD. Many experts believe that the number may be higher, closer to six percent. Millions of people – and their loved ones – struggle with BPD, yet few understand what it is.