Maternal mortality remains a major challenge to health systems worldwide. Reliable information about the rates and trends in maternal mortality is essential for resource mobilisation, and for planning and assessment of progress towards Millennium Development Goal 5 (MDG 5), the target for which is a 75% reduction in the maternal mortality ratio (MMR) from 1990 to 2015. We assessed levels and trends in maternal mortality for 181 countries. We constructed a database of 2651 observations of maternal mortality for 181 countries for 1980-2008, from vital registration data, censuses, surveys, and verbal autopsy studies. We used robust analytical methods to generate estimates of maternal deaths and the MMR for each year between 1980 and 2008. We explored the sensitivity of our data to model specification and show the out-of-sample predictive validity of our methods. We estimated that there were 342,900 (uncertainty interval 302,100-394,300) maternal deaths worldwide in 2008, down from 526,300 (446,400-629,600) in 1980. The global MMR decreased from 422 (358-505) in 1980 to 320 (272-388) in 1990, and was 251 (221-289) per 100,000 livebirths in 2008. The yearly rate of decline of the global MMR since 1990 was 1.3% (1.0-1.5). During 1990-2008, rates of yearly decline in the MMR varied between countries, from 8.8% (8.7-14.1) in the Maldives to an increase of 5.5% (5.2-5.6) in Zimbabwe. More than 50% of all maternal deaths were in only six countries in 2008 (India, Nigeria, Pakistan, Afghanistan, Ethiopia, and the Democratic Republic of the Congo). In the absence of HIV, there would have been 281 500 (243,900-327,900) maternal deaths worldwide in 2008. Substantial, albeit varied, progress has been made towards MDG 5. Although only 23 countries are on track to achieve a 75% decrease in MMR by 2015, countries such as Egypt, China, Ecuador, and Bolivia have been achieving accelerated progress. Bill & Melinda Gates Foundation. Copyright 2010 Elsevier Ltd. All rights reserved.