Background: Non-adherence with antipsychotic medication is a frequently occurring problem, particularly among patients with psychotic disorders. Prior research has generally shown encouraging results for interventions based on 'Contingency Management' (CM), in which desirable behaviour is encouraged by providing rewards contingent upon the behaviour. However, little is known about the application of CM on medication adherence in patients with psychotic disorders. An earlier pilot-study by our study group showed promising results in reducing admission days and increasing adherence. The current study is a randomized controlled trial concerning the effectiveness of a CM procedure called 'Money for Medication' (M4M), aimed at improving adherence with antipsychotic depot medication in psychotic disorder patients. Methods/Design: Outpatients (n = 168) with a psychotic disorder will be randomly assigned to either the experimental group (n = 84), receiving a financial reward for each accepted antipsychotic medication depot, or the control group (n = 84), receiving treatment as usual without financial rewards. Patients are included regardless of their previous adherence. The intervention has a duration of twelve months. During the subsequent six months follow-up, the effects of discontinuing the intervention on depot acceptance will be assessed. The primary goal of this study is to assess the effectiveness of providing financial incentives for improving adherence with antipsychotic depot medication (during and after the intervention). The primary outcome measure is the percentage of accepted depots in comparison to prescription. Secondary, we will consider alternative measures of medication acceptance, i.e. the longest period of uninterrupted depot acceptance and the time expired before depot is taken. Additionally, the effectiveness of the experimental intervention will be assessed in terms of psychosocial functioning, substance use, medication side-effects, quality of life, motivation, cost-utility and patients' and clinicians' attitudes towards M4M. Discussion: This RCT assesses the effectiveness and side-effects of financial incentives in improving adherence with antipsychotic depot medication in patients with psychotic disorders. This study is designed to assess whether M4M is an effective intervention to improve patients' acceptance of their antipsychotic depot medication and to examine how this intervention contributes to patients' functioning and wellbeing.