Objective: To investigate the effect of a (minimally) guided peer support group (GPSG) for people with psychosis on social network, social support, self-efficacy, self-esteem, and quality of life, and to evaluate the intervention and its economic consequences. Method: In a multi-center randomized controlled trial with 56 patients in the peer support group and 50 patients in the control condition, patients were assessed at baseline and after the last meeting at 8 months. Results: The experimental group showed GPSG to have a positive effect on social network and social support compared with the control condition. In the experimental condition, high attenders favored over low attenders on increased social support, self-efficacy, and quality of life. Economic evaluation demonstrated groups to be without financial consequences. The GPSG-intervention was positively evaluated. Conclusion: Peer support groups are a useful intervention for people suffering from psychosis by improving their social network. Copyright © 2008 The Authors.