Partnerships are designed to facilitate the negotiation and delivery of public programmes cutting across the boundaries of a fragmented organisational landscape. This paper makes an empirical contribution to the study of the outcomes of partnership working, reporting results from a detailed United Kingdom case study of mental health services integration. It considers the county-wide establishment of a range of partnerships between a county council and multiple National Health Service organisations under Section 31 of the Health Act (1999), relating to mental health, learning disability, drug and alcohol, and child and adolescent mental health services. Arrangements included: integrated county-wide provision via a partnership trust; pooled commissioning and provision budgets; and joint commissioning arrangements between eight primary care trusts and the county council at a joint commissioning partnership board, supported by a joint commissioning team of officers. The evaluation explores the impact of integrated provision on service users, carers and team staff between 2002 and 2004. A multimethod approach incorporating qualitative and quantitative data was used: individual semistructured interviews and focus groups with staff, users and carers (2004); and questionnaires to team staff to explore role clarity and job satisfaction (2002 and 2004). While users and carers were largely positive towards the new provision, a range of alternative frames of reference towards inpatient episodes were identified, including notions of sanctuary and asylum, as well as lack of privacy and fears over safety. Similarly, there was some ambivalence over the dual focus of the teams on both users and carers. Small improvements overall in team staff scores for role clarity and job satisfaction masked variations between localities; such differences seem less to do with prior experience of partnership working than with recruitment difficulties. Additionally, the study raises methodological issues of relevance to the evaluation of complex social interventions. While partnership forms are themselves relatively easy to define, the attribution of improved outcomes to such arrangements is less straightforward − they are complex social interventions requiring enactment by individuals within specific contexts, typically involving many service changes against a turbulent policy background. Some implications for partnership evaluations are considered.