Around half of the urban population in sub-Saharan Africa live in informal settlements, lacking the basic infrastructure and services on which good health depends. These include safe, regular water piped to homes, good quality sanitation, drains and solid waste collection, electricity, healthcare and emergency services. However, there is very little data available on health problems at the neighbourhood and city scale that are needed to guide action in African cities. Improving official data collection (such as censuses, vital registration systems and healthcare records) will be necessary to address the health risks in informal settlements. In addition, citybased studies of risks and their implications for health can generate relevant data on the most serious health risks facing residents of informal settlements.