BACKGROUND: Violence in Darfur, Sudan, has rendered more than one million people internally displaced. An epidemiological study of the effect of armed incursions on mortality in Darfur was needed to provide a basis for appropriate assistance to internally displaced people. METHODS: Between April and June, 2004, we did retrospective cluster surveys among 215?400 internally displaced people in four sites of West Darfur (Zalingei, Murnei, Niertiti, El Geneina). Mortality recall periods covered both the pre-displacement and post-displacement periods in Zalingei, Murnei, and Niertiti, but not in El Geneina. Heads of households provided dates, causes, and places of deaths, and described the family structure. FINDINGS: Before arrival at displacement sites, mortality rates (expressed as deaths per 10?000 per day), were 5.9 (95% CI 2.2-14.9) in Zalingei, 9.5 (6.4-14.0) in Murnei, and 7.3 (3.2-15.7) in Niertiti. Violence caused 68-93% of these deaths. People who were killed were mostly adult men (relative risk 29.1-117.9 compared with children younger than 15 years), but included women and children. Most households fled because of direct village attacks. In camps, mortality rates fell but remained above the emergency benchmark, with a peak of 5.6 in El Geneina. Violence persisted even after displacement. Age and sex pyramids of surviving populations were skewed, with a deficit in men. INTERPRETATION: This study, which was done in a difficult setting, provides epidemiological evidence of this conflict's effect on civilians, confirming the serious nature of the crisis, and reinforcing findings from other war contexts.