To describe the evolution and current status of the Agincourt field site, Bushbuckridge, in South Africa's rural north-east. A defined subdistrict, with a population of some 60,000 people including Mozambican refugees, in a former 'homeland' area with substantial labour migration. Three phases are described: origins and establishment of the field site; a programme of health systems research underpinned by multi-round (prospective) demographic and health surveillance; and contributions to the University of the North's Dikgale field site. Knowledge of trends in population health (e.g. mortality) is important when shaping the skill base and organisational framework of a district health system. There are valuable opportunities for collaborative research with field sites elsewhere in sub-Saharan Africa, and within South Africa itself. This will be facilitated by a common data model. A country-wide network of field sites, with surveillance capability, would complement the occasional national census and demographic and health survey, and strengthen South Africa's embryonic health information system.