This study examined whether 49 patients from a randomized controlled trial developed insight during therapy and whether insight predicted long-term outcome in short-term dynamic psychotherapy (STDP) and cognitive therapy (CT) for Cluster C personality disorders. Videotaped sessions early and late in treatment were analyzed using the Achievement of Therapeutic Objectives Scale. Patients' level of insight increased significantly during STDP but not CT. After controlling for early symptom change and early insight, insight near the end of therapy predicted improvement of symptom severity and interpersonal functioning during a 2-year follow-up period. These results support the theoretical assumption that insight may be a factor in the change process, central to STDP. Within CT, gain of insight did not predict long-term improvement.