One hundred fifty patients with Panic Disorder (PD) with or without Phobic Avoidance were subdivided into two groups on the basis of presence/absence of derealization and/or depersonalization (D-D) during panic attacks. D-D was found in 34.7% of the sample. By comparing the two groups, the patients with D-D were found to be younger and had an earlier onset of the disorder; they had a higher prevalence of avoidance behavior and a higher severity of the agoraphobic spectrum phobias. They were also more frequently subject to concomitant disorders such as Generalized Anxiety, Obsessive-Compulsive, and depressive symptomatology. The authors have hypothesized a correlation between the presence of D-D during panic attacks and a more frequent clinical evolution toward agoraphobia. This view is supported by finding that D-D in panic attacks corresponds to severer forms of PD, both in terms of the earlier onset of PD, and because PD shows higher levels of anxiety, depression, and disability.