This single-case study describes the mentalization-based therapy (MBT) for a woman diagnosed with severe panic disorder with agoraphobia. The aim of the study is to illustrate how MBT contributes to reducing anxiety symptoms and to strengthening the capacity for reflecting in relation to both self and others as part of developing a more coherent sense of self-identity. The findings indicate a significant therapeutic progress including reduction in anxiety symptoms and a higher function in the patient’s everyday life after MBT. Based on the results of this systematic single-case study, we hypothesize that MBT is a promising therapeutic approach for patients suffering from panic disorder who have not responded to previous treatment. We trace the efficacy of MBT to the therapy’s focus on attachment relationships, affect recognition and management, and working with the patient’s mentalizing capacity.