Reduction of maternal mortality is one of the major goals of several recent international conferences and has been included in the Millennium Development Goals. However, measuring maternal mortality is difficult and complex. Reliable estimates of the dimensions of the problem are not generally available and it is difficult to compare the data obtained from different sources and to assess the overall magnitude of the problem. In response to these challenges, WHO, UNICEF and UNFPA have developed an approach that seeks both to generate estimates for countries with no data and to correct available data for underreporting and misclassification. The approach, with some variations, was used to develop estimates for maternal mortality in 1990 and 1995 and has been used again for generating these estimates for the year 2000. On the basis of the present exercise, the estimated number of maternal deaths in 2000 for the world was 529 000.