The Ouagadougou Health and Demographic Surveillance System (Ouaga HDSS), located in five neighbourhoods at the northern periphery of the capital of Burkina Faso, was established in 2008. Data on vital events (births, deaths, unions, migration events) are collected during household visits that have taken place every 10 months. The areas were selected to contrast informal neighbourhoods (40 000 residents) with formal areas (40 000 residents), with the aims of understanding the problems of the urban poor, and testing innovative programmes that promote the well-being of this population. People living in informal areas tend to be marginalized in several ways: they are younger, poorer, less educated, farther from public services and more often migrants. Half of the residents live in the Sanitary District of Kossodo and the other half in the District of Sig-Nonghin.