The Mental Health Intervention Team (MHIT) programme was developed by New South Wales Police Force (NSWPF) to improve police capacity to respond efficiently and safely to incidents involving persons with a mental illness (PWMI). The programme was initiated in 2008 in three Local Area Commands, wherein 111 officers received enhanced training. It has since been funded for roll-out across the Force. In this paper, we evaluate the success of the MHIT against its key aims: to reduce injury to police and people with a mental illness during their interactions, to enhance awareness amongst police of issues relating to mental illness and how best to mitigate these, to improve interagency collaboration in responding to PWMI and to reduce the amount of unnecessary time police spend on mental health events. We conclude that the MHIT led to increased confidence among police in dealing with mental health-related events, reduced police involvement in transportation of PWMI and improved handover between police and mental health care services. Despite such positive findings, difficulties with interagency cooperation remained, which - we argue - reflects differences in organisational and accountability structures, and concern among NSWPF's partners about the flow-on implications for their own resources. One remedy, we conclude, may lie in a fundamental reconfiguration of public sector responses to PWMI.