Improving living conditions, such as poor housing may be an important means of tackling the socio-economic roots of health inequalities. A systematic review of the health impacts of housing improvement carried out in 2000 identified 18 completed studies and 13 studies approaching completion in 2003. It is now appropriate to update this systematic review to incorporate recently completed studies. Published and unpublished studies dating from 1936, in any language or format, were identified from bibliographic databases, expert consultation and bibliographies. The review included studies where the physical fabric of the housing had improved and which had assessed a change in health status among residents. Improvements to reduce exposure to lead, allergens, or rodent/insect infestation were excluded. Rehousing on medical grounds and housing improvement restricted to furniture adaptations were also excluded. 32 eligible studies of housing improvement were identified dating from 1936; 11 studies used prospective controlled designs. Thirteen studies evaluated housing improvements which were accompanied by wider neighbourhood improvement; 13 studies assessed the health impacts of energy efficiency improvements. Unclear study methods and poor reporting made data interpretation difficult. A preliminary synthesis suggests that small improvements in health, particularly in mental health, were reported although occasionally health outcomes deteriorated following housing improvement. Few studies reported impacts on socio-economic determinants of health. The growing body of impact evaluation in this field is welcome, but it is disappointing that the evidence base for healthy housing policy remains weak.