Personality traits differ among normal people, and one should only diagnose a personality disorder (PD) in the presence of a clear-cut impairment of functioning. Most of these disorders lie on a spectrum with traits, but those that cause prominent symptoms present more often in psychiatry The most clinically important category of PD is borderline personality disorder (BPD), but this condition is widely underdiagnosed. Since these patients often present with depression and/or affective instability, clinicians often see them as suffering from mood disorders, and treat them unsuccessfully with antidepressants. However, this population, which shows repetitive suicidal behavior, needs to be correctly diagnosed to be referred for specialized psychotherapy.