Confronted with a patient with a personality disorder, the oncologist must recognize it and adapt his treatment accordingly. Some pathological character types require interpersonal adjustments to ensure a good understanding of the cancer disease and also to obtain the best compliance with supportive care. Given the fact that specific pharmacological treatment does not exist, collaboration between oncologists and the psycho-oncology team is paramount. The interaction between the somatic disease and the psychiatric disorder demand collaboration among caregivers sharing explanations and recommendations. Clinical examples will illustrate each personality disorder and will focus on the several problems raised by the psychiatric disorder. Treatment principles will be addressed in a second section.