Patients with deliberate self harm syndrome and with factitious disorders often describe depersonalisation phenomena, during which they have a diminished pain sensitivity or analgesia. The self-mutilating act can stop the depersonalisation temporarily. Concerning the psychodynamic processes there are common traits between depersonalisation and self-mutilation. The connections between depersonalisation and self-mutilating behaviour are described. Depersonalisation is understood as a defense mechanism, ranging between mature and immature defense mechanisms. An illustrative case is demonstrated.