The issue of housing and health has received growing attention in recent years. This article reviews why this has been the case and presents the results of the authors' study of housing and health in two areas of West Belfast. A large scale household survey was carried out in Divis Flats and part of the Twinbrook estate, both deprived areas of public sector housing, to compare health and housing conditions. The health of children in Divis is shown to be much worse than the health of children in Twinbrook. Respiratory conditions, diarrhoea, vomiting and psychological distress were particularly common. The health of adults in Divis was also markedly worse than in Twinbrook, and the health of women generally worse than men. The authors conclude that Divis Flats is a contemporary public sector slum and support the case for clearance and rehousing. However, it is argued that the health problems of Divis are one, extreme, manifestation of a wider problem of ill health in low income, ‘mass housing’ areas.