Patients with personality disorders are common. They often have co-morbid mental and physical illnesses, poor quality of life, and severe social impairment. Yet, these disorders of personality are often undiagnosed. A detailed and carefully taken history and, at best, a structured interview are important for a valid diagnosis, description of dysfunctional traits and for the assessment of severity. An initial psychotherapeutic case formulation is important to enhance alliance and adherence. In case of psychiatric co-morbidities, depending on their severity, they should be treated first.