SummarySurvey data are presented from a nationwide survey of the health of schoolchildren in Chad. The country was stratified into distinct ecological zones based on satellite sensor environmental data. Twenty schools were visited and 1024 children aged between 6 and 15 years were included in the study. The overall prevalence of stunting, underweight, anaemia and goitre was 18.7, 16.5, 25.1 and 23.3%, respectively. Schistosoma haematobium, Schistosoma mansoni and hookworm were the only helminth species found with prevalences of 13.2, 1 and 32.7%, respectively. A greater proportion of boys were stunted, underweight, anaemic and infected with S. haematobium and hookworm than girls. Older children were more stunted, underweight and infected with S. haematobium and hookworm than younger children, but less anaemic. The prevalence of infection showed marked geographical heterogeneity, with hookworm prevalence being highest in the Sudanian and tropical zone, and S. haematobium being most prevalent in the Sahelian zone and the Logone and Chari basins in the west of the country. These data show that there is a high prevalence of helminth infection in Chad, but that treatment for S. haematobium and hookworm should be targeted to different geographical areas.