Research indicates that posttraumatic stress disorder (PTSD) is associated with high rates of comorbid psychiatric diagnoses. Yet, it remains unknown whether PTSD is associated with greater comorbidity relative to patients with other anxiety disorders. This study examined prevalence of comorbid anxiety disorders with PTSD relative to other disorders among a treatment-seeking population. Patients with PTSD (n = 83) evidenced greater overall comorbidity as compared to patients with other anxiety (n = 151) or Axis I (n = 73) disorders. Compared to patients with panic disorder, patients with PTSD were more likely to be diagnosed with depression and social phobia, but not other anxiety disorders. Extent of anxiety disorder comorbidity was not related to PTSD severity. These findings are discussed in terms of their relevance for treatment of PTSD.