The aims of this study were to examine whether a change in overall defensive functioning during treatment a) would predict change in symptom distress during the course of treatment and follow-up and b) would be greater in short-term dynamic therapy than in cognitive therapy. Patients (N = 50) who met criteria for cluster C personality disorders were randomized to 40 weekly sessions of short-term dynamic therapy or cognitive therapy. Video recordings of a pretreatment interview and therapy session 36 were evaluated using the Defense Mechanisms Rating Scales. Symptom distress was measured using the revised version of Symptom Checklist-90. Change in overall defensive functioning during treatment predicted change in symptom distress from pretreatment to 2 years after treatment. Both treatment groups showed significant changes in defensive functioning toward greater adaptability but without any significant differences between the short-term dynamic therapy and cognitive therapy groups in a sample of patients with cluster C personality disorders.