Since the recognition (DSM-IV; American Psychiatric Association, 1994) of life-threatening illnesses as a stressor that can precipitate posttraumatic stress disorder (PTSD), research has focussed on the issue of PTSD following cancer. Although the utility of a trauma framework has been questioned, understanding symptoms associated with PTSD such as intrusive cognitions may be critical in understanding psychological distress in cancer patients. Research has found that cancer patients experience negative intrusive thoughts, which are associated with marked distress. However, studies have rarely explored the content or nature of intrusions. In addition to verbal intrusions, intrusive memories of illness have been reported in cancer patients. More recently, intrusive imagery has been found in populations of anxious patients and reported to have a causal role in the maintenance of anxiety. Based on the recognition of cancer as a protracted experience involving multiple stressors, future-oriented visual intrusions, as well as intrusive memories and thoughts may play a role in psychological functioning. Chapter 1 is an overview of the literature assessing the presence of posttraumatic stress and posttraumatic stress symptoms in cancer patients. Chapter 2 is a cross-sectional study which showed that anxious prostate cancer patients (N=65) were significantly more likely to report intrusive cognitions compared to matched non-anxious (N=65) prostate cancer patients. Intrusive cognitions were frequent, uncontrollable and associated with significant distress and maladaptive adjustment. Chapter 3 is a cross-sectional study (N=139), which showed that factors such as how patients appraise intrusive cognitions affects anxiety severity and intrusion-related distress, after controlling for intrusion frequency. Chapter 4 provides a discussion of the use of imagery in psychological therapy and how imagery has been used with cancer patients in therapy. Chapter 5 presents two single-case studies of cancer patients completing a short therapy for anxiety, imagery rescripting, aimed at reducing negative properties of intrusive cognitions whilst also alleviating anxiety and depression. The final chapter provides a general discussion of the thesis and presents ideas for future research.