Patients with acute panic disorder (PD) use a more maladaptive pattern of defense mechanisms. This study investigated the use of defense mechanisms by patients with acute symptomatic PD and those in complete remission. Thirty-three patients and 33 controls were evaluated by the Mini International Neuropsychiatric Interview. The defense mechanisms were evaluated by the Defense Style Questionnaire at the beginning of the study and after 16 weeks of sertraline treatment. Panic disordered patients used more neurotic (4.6 vs. 3.6; p = 0.003) and immature (3.6 vs. 3.0; p = 0.024) defenses at baseline. Patients who achieved complete remission (N=25) differed from the control group in the use of neurotic defenses at the baseline (4.4 vs. 3.6; p = 0.033). After treatment, they showed a reduction in the use of neurotic (4.4 vs. 3.7; p=0.014) and immature (3.4 vs. 3.1; p = 0.019) defenses. Defense mechanisms in PD are influenced by the presence of symptoms, severity, and outcome of the disease.