This dissertation presents an etiological model for pathological dissociation based on attachment theory. From this perspective, attachment and intersubjective disorganization processes may be considered a hidden trauma . The new ideas from intersubjectivity theory and research has widened the scope of attachment theory. This widened version of attachment theory stresses the central role of intersubjective processes, not only in the organization of the attachment system, but also in the organization of the self. Longitudinal prospective studies show a remarkable relation between infant disorganized attachment and pathological dissociation in young adults. The results from these studies, analyzed from an attachment theory perspective, support a proposition for redefinition of early trauma. Current studies suggest that the stress generated by subtle parent-infant disruptive affective communication mechanisms may give rise to disorganization processes that affect the development of the attachment system and of the self. Such processes may be the beginning of a developmental trajectory towards pathological dissociation.