This paper is based on a keynote address delivered at the diamond jubilee congress of the Royal College of Nursing at Harrogate, England, on 5 April 1976. After discussing the functional and dysfunctional aspects of aggression in society, the author reviews the recent literature, citing British and American studies conducted in psychiatric, mental handicap and general hospitals. The effects of environment and disease processes are identified and the implications of violence in patients are discussed, particularly the implications for trained nurses and nursing students. The author contends that it is violence rather than aggression that needs to be eradicated from society and pleads for more research-based knowledge about violence, arguing that ‘knowledge must come before treatment’.