The risk of a woman dying as a result of pregnancy or childbirth during her lifetime is about one in six in the poorest parts of the world compared with about one in 30 000 in Northern Europe. Such a discrepancy poses a huge challenge to meeting the fifth Millennium Development Goal to reduce maternal mortality by 75% between 1990 and 2015. Some developed and transitional countries have managed to reduce their maternal mortality during the past 25 years. Few of these, however, began with the very high rates that are now estimated for the poorest countries-in which further progress is jeopardised by weak health systems, continuing high fertility, and poor availability of data. Maternal deaths are clustered around labour, delivery, and the immediate postpartum period, with obstetric haemorrhage being the main medical cause of death. Local variation can be important, with unsafe abortion carrying huge risk in some populations, and HIV/AIDS becoming a leading cause of death where HIV-related mortaliy rates are high. Inequalities in the risk of maternal death exist everywhere. Targeting of interventions to the most vulnerable--rural populations and poor people--is essential if substantial progress is to be achieved by 2015.