Most dissociative disorders have in common that patients afflicted by them often report a history of childhood trauma and that the severity of the dissociative symptoms is often significantly correlated with the severity of childhood trauma reported (Lochner, Seedat et al. 2004, Bob, Susta et al. 2005, Molina-Serrano, Linotte et al. 2008, Imperatori, Innamorati et al. 2017). Childhood maltreatment is also a risk factor for posttraumatic stress disorder (PTSD). Accordingly, dissociative symptoms are regularly reported by patients suffering from PTSD (Hopper, Frewen et al. 2007, Daniels, Coupland et al. 2012, Steuwe, Lanius et al. 2012) and up to 25% of patients with PTSD following childhood abuse can be classified as belonging to the dissociative subtype (Steuwe, Lanius et al. 2012, Wolf, Miller et al. 2012). Dissociation in PTSD as well as before mentioned patient samples typically involves transient episodes of depersonalization and derealization (but not identity confusion or amnesia for current events). However, in depersonalization/derealization disorder, the same set of symptoms occurs chronically, rendering the patients severely impaired. Interestingly, while phenomenologically similar, these symptom sets seem to be associated with divergent neurobiological alterations. This chapter will summarize the current knowledge regarding structural and functional brain alterations associated with dissociation - both in patients suffering from short-lived dissociation such as in PTSD and in chronic states as seen in patients with dissociative disorders.