BackgroundThis study aims for health gain and cost reduction in the care for people with long-term non-psychotic psychiatric disorders. Present care for this population has a limited evidence base, is often open ended, little effective, and expensive. Recent epidemiological data shows that 43.5% of the Dutch are affected by mental illness during their life. About 80% of all patients receiving mental health services (MHS) have one or more non-psychotic disorders. Particularly for this group, long-term treatment and care is poorly developed. Care As Usual (CAU) currently is a form of low-structured treatment/care. Interpersonal Community Psychiatric Treatment (ICPT) is a structured treatment for people with long-term, non-psychotic disorders, developed together with patients, professionals, and experts. ICPT uses a number of evidence-based techniques and was positively evaluated in a controlled pilot study.Methods/DesignMulti-centre cluster-randomized clinical trial: 36 professionals will be randomly allocated to either ICPT or CAU for an intervention period of 12 months, and a follow-up of 6 months. 180 Patients between 18–65 years of age will be included, who have been diagnosed with a non-psychotic psychiatric disorder (depressive, anxiety, personality or substance abuse disorder), have long-term (>2 years) or high care use (>1 outpatient contact per week or >2 crisis contacts per year or >1 inpatient admission per year), and who receive treatment in a specialized mental health care setting. The primary outcome variable is quality of life; secondary outcomes are costs, recovery, general mental health, therapeutic alliance, professional-perceived difficulty of patient, care needs and social contacts.DiscussionNo RCT, nor cost-effectiveness study, has been conducted on ICPT so far. The empirical base for current CAU is weak, if not absent. This study will fill this void, and generate data needed to improve daily mental health care.Trial registrationNetherlands Trial Register (NTR): 3988. Registered 13th of May 2013.