Starting with a view of war as a significant population health problem, this article explores the roles of health workers in relation to violent conflict. Four different roles are identified, defined by goals and values--military, development, humanitarian and peace. In addition, four dimensions of health work are seen as cross-cutting factors influencing health work in violent conflict-- whether the health worker is an insider or outsider to the conflict, whether they are oriented to primary, secondary or tertiary prevention of the mortality and morbidity of war, whether they take an individual clinical or a population health approach, and whether they are oriented to policy and whole-sector change or not. This article explores the nature of these roles, the influence of these cross-cutting dimensions, the challenges of each role and finally commonalities and possibilities for cooperation between roles.