High dissociation has been linked to severe psychopathology. However, relatively little is known about the impact of dissociation on treatment outcome. We sought to examine (a) whether initial levels of dissociation predicted treatment outcome, (b) whether changes in dissociation were associated with changes in other forms of psychopathology, and (c) to what extent individuals with high initial dissociation reported meaningful symptom improvement. Participants (N = 174) were patients at an outpatient trauma clinic. Initial dissociation was significantly associated with general symptom severity. Change in dissociation was significantly and positively associated with change in posttraumatic stress disorder, depression, suicidal ideation, and self-harm. Approximately 40% of high dissociators demonstrated reliable decreases in dissociation during treatment.