The Bandafassi Health and Demographic Surveillance System (Bandafassi HDSS) is located in south-eastern Senegal, near the borders with Mali and Guinea. The area is 700 km from the national capital, Dakar. The population under surveillance is rural and in 2012 comprised 13 378 inhabitants living in 42 villages. Established in 1970, originally for genetic studies, and initially covering only villages inhabited by one subgroup of the population of the area (the Mandinka), the project was transformed a few years later into a HDSS and then extended to the two other subgroups living in the area: Fula villages in 1975, and Bedik villages in 1980. Data have been collected through annual rounds since the project first began. On each visit, investigators review the composition of all the households, checking the lists of people who were present in each household the previous year and gathering information about births, marriages, migrations and deaths (including their causes) since then. One specific feature of the Bandafassi HDSS is the availability of genealogies.