In Bangladesh, the health risks of unplanned urbanization are disproportionately shouldered by the urban poor. At the same time, affordable formal primary care services are scarce, and what exists is almost exclusively provided by non-government organizations (NGOs) working on a project basis. So where do the poor go for health care? A health facility mapping of six urban slum settlements in Dhaka was undertaken to explore the configuration of healthcare services proximate to where the poor reside. Three methods were employed: (1) Social mapping and listing of all Health Service Delivery Points (HSDPs); (2) Creation of a geospatial map including Global Positioning System (GPS) co-ordinates of all HSPDs in the six study areas and (3) Implementation of a facility survey of all HSDPs within six study areas. Descriptive statistics are used to examine the number, type and concentration of service provider types, as well as indicators of their accessibility in terms of location and hours of service. A total of 1041 HSDPs were mapped, of which 80% are privately operated and the rest by NGOs and the public sector. Phamacies and non-formal or traditional doctors make up 75% of the private sector while consultation chambers account for 20%. Most NGO and Urban Primary Health Care Project (UPHCP) static clinics are open 5–6 days/week, but close by 4–5 pm in the afternoon. Evening services are almost exclusively offered by private HSDPs; however, only 37% of private sector health staff possess some kind of formal medical qualification. This spatial analysis of health service supply in poor urban settlements emphasizes the importance of taking the informal private sector into account in efforts to increase effective coverage of quality services. Features of informal private sector service provision that have facilitated market penetration may be relevant in designing formal services that better meet the needs of the urban poor.