People with BPD are often also diagnosed with eating disorders, major depression, dual diagnosis, post traumatic stress disorder attention deficit disorder, and bi-polar disorder.

We conducted a study of a sample patients admitted to our residential treatment program that came to us with a diagnosis of BPD. We tallied the number of other diagnoses they had been given prior to their admission. Of 274 people diagnosed with BPD in our sample we found that the top 10 co-existing diagnoses were:

These co-existing diagnoses strongly suggest that the core emotional experience of BPD is one of depressive and anxious feelings driven by stressful experiences both past and present and self-medicated with drugs and alcohol.

People with BPD will often pick up the symptoms of other patients complicating the diagnosis of co-existing conditions. Sometimes the symptoms will appear for a transient period of time and then disappear. For example, a BPD patient may develop bulimia for several weeks and once it becomes the focus of treatment the symptoms go away only to be replaced by sexual acting out or depression. For this reason it is important to take a complete clinical history to get as comprehensive a picture as possible of the person's condition. If BPD is present it must be treated effectively if lasting improvement to other symptoms is to occur.