Background: Men with prostate cancer experience elevated levels of anxiety and depression, with some previous data suggesting that this is due to loss of previously-available social and personal reinforcing pleasant activities and abilities. Little is currently known about the range of activities/abilities that these patients lose, leaving open the question of how to best target lifestyle changes designed to help them overcome these negative effects on their mental health. This study used personal interviews to gather details of the pattern of lost activities/abilities from a sample of men with prostate cancer so that a self-report questionnaire might be developed for use in large-scale studies of the 'causal map' of anxiety and depression among these patients. Method: Ten men who had received a diagnosis of, and treatment for, prostate cancer during the previous 30 months were voluntary participants in a personal interview that tapped their experiences of the diagnostic and treatment processes and the effects of these upon their lifestyles. Results: Data confirmed the primary effect of lost activities/abilities (particularly sexual) on these men as being causal vectors for the development of anxiety and depression. Conclusion: As well as providing an insight into the experiences of these prostate cancer patients, the findings reported here allowed for the development of a 50-item self-report questionnaire for exploration of the causal factors underlying anxiety and depression among prostate cancer patients.