Posttraumatic nightmares (PTN) are a frequent symptom after a traumatic event and often play part in the psychopathology of patients with borderline personality disorder (BPD). Imagery rehearsal therapy (IRT) currently offers the best evidence for an effective treatment to reduce PTNs, although high drop‐out rates are common. Art therapy in IRT may counteract this, by its indirect, nonverbal, and often playful approach that helps to break through avoidance. This case study focusses on the perception of a patient with BPD in an art therapy based IRT treatment for patients with PTNs. It tells the story of Aurelia, a 40‐year‐old woman who, within this treatment, processes traumatic contents of her childhood like physical and sexual violence, but also current interactional problems that manifest themselves in her nightmares. Following the IR‐AT treatment for PTNs Aurelia noticed a reduction in her nightmares, was less afraid of them and felt calmer towards her trauma. She expressed herself in the art medium and by this developed more self‐efficacy. Her process resulted in an integration of the trauma and a perceived decrease in borderline symptoms. Future research can build on this basis to further explore the mechanisms and effects of IR‐AT for PTNs.