The aim of the study was to investigate and compare anxiety sensitivity measurements and panic-agoraphobic spectrum symptoms in patients diagnosed with panic disorder and in their first degree relatives. Eighty patients who were on followup or recently diagnosed as panic disorder in a university faculty of medicine psychiatry department and their first degree relatives (80 siblings) were included after clinical evaluation. The patients were assessed with socio-demographic information form, Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-1), Anxiety Sensitivity Index (ASI), State-Trait Anxiety Inventory (STAI), Beck Depression Inventory (BDI), Panic-Agoraphobic Scale (PAS) and Lifetime Panic-Agoraphobic Spectrum Self Report (PAS-SR lifetime); and their siblings were assessed with socio-demographic information form, SCID-1, ASI, STAI, BDI, and PAS-SR lifetime. According to the results of the study, it was determined that the ASI scores of the patients were statistically significantly higher than the scores of their siblings (p<0.01). In addition, patients scored significantly higher on the PAS-SR lifetime scale than siblings (p<0.01). Inclusion of BDI scores in covariant analysis has made no change in the difference among study groups in level of anxiety sensitivity and degree of panic agoraphobic spectrum. As a conclusion, in this study, it was found that anxiety sensitivity and spectrum symptoms, which are two variables investigated as endophenotypic features in the first degree relatives in the panic disorder, differ from the patient group in terms of severity and frequency.