SUMMARYThree issues characterise the background to the MECCA study: A) Throughout Europe, most patients with severe forms of psychotic disorders are cared for in the community. The challenge now is to make processes in community mental health care more effective. B) There are widespread calls to implement regular outcome measurement in routine settings. This, however, is more likely to happen, if it provides a direct benefit to clinicians and patients. C) Whilst user involvement is relatively ?" easy to achieve on a political level, new mechanisms may have to be established to make the views of patients feed into individual treatment decisions. The MECCA study is a cluster randomised controlled trial following the same protocol in community mental health teams in six European countries. In the experimental group, patients' subjective quality of life, treatment satisfaction and wishes for different or additional help are assessed in key worker-patient meetings every two months and intended to inform the therapeutic dialogue and treatment decisions. The trial tests the hypothesis that the intervention – as compared to current best standard practice – will lead to a better outcome in terms of quality of life and other criteria in patients with psychotic disorders over a one year period. This more favourable outcome is assumed to be mediated through different treatment input based on more appropriate joint decisions or a more positive therapeutic relationship in line with a partnership model of care or both. Moreover, the study will hopefully reveal new insights into how therapeutic processes in community mental health care work and how they can be optimised.