This study's aim was to prospectively examine and identify a model of demographic, clinical, and attitudinal variables that impact improvement among patients with panic disorder. Subjects were 232 primary care patients meeting criteria for DSM-IV panic disorder. Eligible patients were randomly assigned to a collaborative care intervention or to treatment as usual. Assessments occurred at 3-month intervals during the course of 1 year. In final multivariate logistic regression models, patients with higher anxiety sensitivity and higher neuroticism scores at baseline were less likely to show clinical improvement (using a criterion of 20 or less on the Anxiety Sensitivity Index) at 3 months. Those who were non-white, had higher anxiety sensitivity, and higher overall phobic avoidance at baseline were less likely to show clinical improvement at 12 months. A greater understanding of these predictors may help clinicians identify who is at greatest risk for persistent panic-related symptoms and to plan the intensity of interventions accordingly.