Health-related data provide the basis of policy in many domains. By using a methodology specifically designed to gather data about any form of violence and its impact, violence affecting health-care personnel, health-care facilities, and the wounded and sick in these facilities can be quantified on an objective basis. The impact of this form of violence and its accompanying insecurity goes beyond those directly affected to the many who are ultimately denied health care. Reliable data about both the violence affecting health-care personnel and facilities and the 'knock-on' effects of this violence on the health of many others have a critical role to play in influencing the policies of all stakeholders, including governments, in favour of greater security of effective and impartial health care in armed conflict and other emergencies. The International Committee of the Red Cross has undertaken a study that attempts to understand on a global basis the nature and impact of the many different kinds of violence affecting health care. Keywords: health-care data, Health Care in Danger, violence against health care, denial of access to health care, Sixteen-Country Study, insecurity of health care.