Data for trends in contraceptive use and need are necessary to guide programme and policy decisions and to monitor progress towards Millennium Development Goal 5, which calls for universal access to contraceptive services. We therefore aimed to estimate trends in contraceptive use and unmet need in developing countries in 2003, 2008, and 2012 . We obtained data from national surveys for married and unmarried women aged 15-49 years in regions and subregions of developing countries. We estimated trends in the numbers and proportions of women wanting to avoid pregnancy, according to whether they were using modern contraceptives, or had unmet need for modern methods (ie, using no methods or a traditional method). We used comparable data sources and methods for three reference years (2003, 2008, and 2012). National survey data were available for 81-98% of married women using and with unmet need for modern methods. The number of women wanting to avoid pregnancy and therefore needing effective contraception increased substantially, from 716 million (54%) of 1321 million in 2003, to 827 million (57%) of 1448 million in 2008, to 867 million (57%) of 1520 million in 2012. Most of this increase (108 million) was attributable to population growth. Use of modern contraceptive methods also increased, and the overall proportion of women with unmet need for modern methods among those wanting to avoid pregnancy decreased from 29% (210 million) in 2003, to 26% (222 million) in 2012. However, unmet need for modern contraceptives was still very high in 2012, especially in sub-Saharan Africa (53 million [60%] of 89 million), south Asia (83 million [34%] of 246 million), and western Asia (14 million [50%] of 27 million). Moreover, a shift in the past decade away from sterilisation, the most effective method, towards injectable drugs and barrier methods, might have led to increases in unintended pregnancies in women using modern methods. Achievement of the desired number and healthy timing of births has important benefits for women, families, and societies. To meet the unmet need for modern contraception, countries need to increase resources, improve access to contraceptive services and supplies, and provide high-quality services and large-scale public education interventions to reduce social barriers. Our findings confirm a substantial and unfinished agenda towards meeting of couples' reproductive needs. UK Department for International Development, the Bill & Melinda Gates Foundation, and the UN Population Fund (UNFPA). Copyright © 2013 Elsevier Ltd. All rights reserved.