Background Although the literature on effects of armed conflict on population health is extensive, detailed assessments of effects on public health ‘systems’ are few. This article aims to help address this deficit through the medium of a case study on Yemen, describing health system and health outcome performance prior to the internationalisation of the conflict there in March 2015, before assessing the impact of war on health system functionality since that time.

Method Review of peer- and non-peer reviewed literature from 2005 to 2016 from academic sources, multilateral organizations, donors and governmental and non-governmental organizations, augmented by secondary data analysis.

Results Despite significant health system weaknesses and structural vulnerabilities pre-conflict, there were important improvements in selected health outcome measures in Yemen up to early 2015 (life expectancy, and infant and maternal mortality, e.g.), partly driven by a fragile health sector that was heavily reliant on out-of-pocket expenditure, and hampered by weak service penetration especially in rural areas. High intensity conflict has resulted in rising mortality and injury rates since March 2015, the first decline in life expectancy and increase in child and maternal mortality in Yemen for some years, and worsening levels of malnutrition. Service delivery has become increasingly challenging in the context of a funding crisis, destruction of health facilities, widespread shortages of essential medicines and equipment across the country, and governance fragmentation.

Conclusion Conflict in Yemen has resulted in humanitarian disaster on a wide scale in a short period of time, and crippled an already weak health system. Important areas of uncertainty remain, however, including the scale of health worker flight, and the extent to which alternative providers have stepped in to fill widening service gaps as the conflict has unfolded. Planning for longer-term health system reconstruction should begin as soon as possible.