Anxiety and avoidance dimensions of adult attachment insecurity were tested as moderators of treatment outcome for interpersonal psychotherapy (IPT) and cognitive-behavioral therapy (CBT). Fifty-six participants with major depression were randomly assigned to these treatment conditions. Beck Depression Inventory-II, Six-Item Hamilton Rating Scale for Depression scores, and remission status served as outcome measures. Patients higher on attachment avoidance showed significantly greater reduction in depression severity and greater likelihood of symptom remission with CBT as compared with IPT, even after controlling for obsessive-compulsive and avoidant personality disorder symptoms. Results were replicated across treatment completers and intent-to-treat samples. These results suggest that it is important to consider the interaction between attachment insecurity and treatment type when comparing efficacy of treatments.