Post-abortion care (PAC), an innovation for treating women with complications of unsafe abortion, has been introduced in public health systems around the world since the 1994 International Conference on Population and Development (ICPD). This article analyzes the process of scaling-up two of the three key elements of the original PAC model: providing prompt clinical treatment to women with abortion complications and offering post-abortion contraceptive counseling and methods in Bolivia and Mexico. The conceptual framework developed from this comparative analysis includes the environmental context for PAC scale-up; the major influences on start-up, expansion, and institutionalization of PAC; and the health, financial, and social impacts of institutionalization. Start-up in both Bolivia and Mexico was facilitated by innovative leaders or catalyzers who were committed to introducing PAC services into public health care settings, collaboration between international organizations and public health institutions, and financial resources. Important processes for successful PAC expansion included strengthening political commitment to PAC services through research, advocacy, and partnerships; improving health system capacity through training, supervision, and development of service guidelines; and facilitating health system access to essential technologies. Institutionalization of PAC has been more successful in Bolivia than Mexico, as measured by a series of proposed indicators. The positive health and financial impacts of PAC institutionalization have been partially measured in Bolivia and Mexico. Other hypotheses--that scaling-up PAC will significantly reduce maternal mortality and morbidity, decrease abortion-related stigma, and prepare the way for efforts to reform restrictive abortion laws and policies--have yet to be tested.