As new organizations with responsibility for the health and health care of their local populations, primary care trusts (PCTs) need to engage with patients and the wider public. This paper identi. es the challenges faced by PCTs in implementing patient and public involvement and reports on a qualitative study of four PCTs in one health district. Findings from two pieces of data collection are reported on: an audit of community involvement activity and 16 semi-structured interviews with individuals working in the PCTs. The findings show that organizational capacity for undertaking patient and public involvement activities increased considerably over an 18 month period. The PCTs were found to be engaging with individuals and groups from the community and voluntary sector through a range of different structures and processes. Considerable commitment to patient and public involvement was reported but there were concerns over implementation. A number of influencing factors were identified including national policy, organizational factors, leadership, workload, access to experienced involvement workers and the pattern of local community activity. The paper discusses the implications for the development of patient and public involvement in PCTs including the importance of cultural change and the need for organizational development. The potential for PCTs to be involved in a range of participatory activities and to work with other partner organizations in localities is also discussed. The paper concludes that, despite challenges, progress can be made in implementing patient and public involvement as a mainstream activity in PCTs.