The present study used two single case studies to evaluate clinicalimprovement as a result of cognitive behavior therapy in panic disorderwith or without agoraphobia (PDA). A special emphasis was placed on assessingthe reduction in catastrophic cognitions, which are considered to be of primeimportance in PDA. Multiple measures were employed, during pre and posttreatment and at a six month follow-up. Data from self-report questionnaires,physiological measures and cognitive sampling during in vivo exposurewere used. Convergent results demonstrated clinical improvement and supportedthe importance of catastrophic cognitions in the process of change for treatmentoutcome of PDA.