Trust is central to good relationships between patients and health-care providers because, firstly, patient uncertainty about health conditions requires them to have confidence in a doctor's motives and decisions, and secondly, trust facilitates communication and patient focus which encourages people to utilise health services. This paper focuses on patient trust because of its effect on treatment-seeking behaviour and the treatment costs incurred by poor households. Drawing from other studies the paper distinguishes between trust based on the perceived technical competence of the provider, and on inter-personal dimensions of quality of care. Trust is also analysed at two inter-related levels: personal trust that is built through face-to-face encounters with providers; and more abstract institution-level trust. The paper applies these notions of trust to examine treatment-seeking behaviour in two poor urban communities in Colombo, Sri Lanka. Household survey data and qualitative data show that people from a range of income groups preferred to use public providers for more serious illnesses because public services were free and they trusted the technical competence of public providers at both a personal and institutional level. The data also show, however, that inter-personal quality of care was lacking in the public sector and that residents from the two communities, including a considerable minority of the poorest, preferred to use private providers for moderate acute illnesses. People were willing to pay for private services because it saved time, doctors listened and they could build better relationships with private doctors. Despite the strengths of Sri Lanka's public health sector, poor relationships act as an access barrier and push a range of income groups to the private sector. The threat to access and affordability posed by these poor relationships should be the focus of current reform debates.