Poor urban women in Latin America have previously been characterised by their involvement in collective survival strategies. This paper uses the theme of professionalisation to re-conceptualise grassroots women's ongoing community organising by recognising the distinct expertise that these women have accumulated during their many years of voluntary activism. I consider how women health promotion activists construct a particular brand of professionalism, based on practical experience and informal training. This professionalism involves engaging in a balancing act between being ‘experts’ in reproductive health whilst maintaining their status as community women on which their success as health promoters depends. The paper defines this process of grassroots professionalisation as one which simultaneously contests, and yet is itself a product of, neoliberal development imperatives. This construction of a particularly grassroots professionalisation allows for a more nuanced understanding of expertise within everyday political geographies and at different scales of the development process.