Although much has been written about 'aggression' from a variety of viewpoints, little systematic information has been gathered about what nurses see as 'aggression'. Also, it is not clear from previous reports just how important horizontal violence is for nurses compared with the other "aggressions' encountered at work. A qualitative approach was adopted as this was an initial exploratory study to describe nurses' views regarding the nature and extent of aggression in the clinical setting. A total of 29 nurses were interviewed. Findings indicate that nurses are most concerned about their colleagues' aggression towards them. Colleague abuse ranged from non-verbal innuendo to physical assault. Nurse managers were criticized for failing to implement supportive structures when aggression did arise (from colleagues or others) or to take appropriate action to prevent its recurrence. On a practical level much of the aggression reported can be seen as a breakdown in 'relationship rules', i.e. staff failed to respect each other's privacy, were unwilling to help out, keep confidences and so on.