Self-esteem variability is often associated with poor functioning. However, in disorders with entrenched negative views of self and in a context designed to challenge those views, variable self-esteem might represent a marker of change. We examined self-esteem variability in a sample of 27 patients with Avoidant and Obsessive–Compulsive Personality Disorders who received Cognitive Therapy. A therapy coding system was used to rate patients’ positive and negative views of self expressed in the first ten sessions of a 52-week treatment. Ratings of negative (reverse scored) and positive view of self were summed to create a composite score for each session. Self-esteem variability was calculated as the standard deviation of self-esteem scores across sessions. More self-esteem variability predicted more improvement in personality disorder and depression symptoms at the end of treatment, beyond baseline and average self-esteem. Early variability in self-esteem, in this population and context, appeared to be a marker of therapeutic change.