There has been considerable debate in the last decade about whether or not family planning programmes in developing countries reduce fertility or improve socio-economic outcomes. This article provides new evidence by studying the expansion of one of the world's oldest and largest family planning organisations - Profamilia of Colombia. It finds that family planning explains less than 10% of Colombia's fertility decline during its demographic transition. As in wealthy countries, however, lowering the costs of first birth postponement produced important socio-economic gains, enabling young women to obtain more education and to work more and live independently later in life.