Excessive comorbidity within personality disorders and other psychiatric disorders is a perennial problem in psychiatric diagnosis and treatment. Questions of etiology, disorder hierarchies, and treatment decisions are problems clinicians face on a daily basis. From a pragmatic view, the presence of multiple psychiatric disorders co-occurring within the context of a personality disorder can be viewed as proxy for psychiatric severity particularly as it relates to impairments in interpersonal relating, affective instability, and impulsivity. By extension, impairments in the above facets of functioning can alert clinicians to a range of potential treatment challenges including forming and maintaining a treatment alliance, sustaining treatment adherence, and targeting symptoms for medication treatment. Evidence from high-quality efficacy studies demonstrate significant, and in some cases lasting, symptom and behavioral change, especially for patients diagnosed with borderline personality disorder.