Both the number of patients with dissociative disorder and that of those with self-injury have been increasing since the end of the twentieth century,suggesting that dissociation and self-injury might be closely related. When dissociative disorder coexists with self-injury, it implies self-punishment and a wish to be understood by others. Although many cases of selfinjury observed since 2000 lacked traumatic experiences and were not accompanied by pathological dissociative symptoms,the patients did have dissociative tendencies. According to the results of our study examining self-injury in patients with eating disorders, we observed that self-injury,dissociative tendency and insulation from others are related to each other. This suggests that affects,sensations and representations are dissociated,losing their normal response order,and that the pervasive idea that “pain＝secure”is formed in a patient from childhood based on influence from their parents. Self-injury appears to be an activation of this pervasive idea that is triggered by a stressful situation,when the dissociative psychological segmentation of effects and their representations are present in the background.