Background: Hospitalization is a common method to intensify care for patients experiencing a psychiatric crisis. A short-term, specialised, out-patient crisis intervention by a Crisis Resolution Team (CRT) in the Netherlands, called Intensive Home Treatment (IHT), is a viable intervention which may help reduce hospital admission days. However, research on the (cost-)effectiveness of alternatives to hospitalisation such as IHT are scarce. In the study presented in this protocol, IHT will be compared to care-as-usual (CAU) in a randomized controlled trial (RCT). CAU comprises low-intensity outpatient care and hospitalisation if necessary. In this RCT it is hypothesized that IHT will reduce inpatient days by 33% compared to CAU while safety and clinical outcomes will be non-inferior. Secondary hypotheses are that treatment satisfaction of patients and their relatives are expected to be higher in the IHT condition compared to CAU. Methods: A 2-centre, 2-arm Zelen double consent RCT will be employed. Participants will be recruited in the Amsterdam area, the Netherlands. Clinical assessments will be carried out at baseline and at 6, 26 and 52 weeks post treatment allocation. The primary outcome measure is the number of admission days. Secondary outcomes include psychological well-being, safety and patients' and their relatives' treatment satisfaction. Alongside this RCT an economic evaluation will be carried out to assess the cost-effectiveness and cost-utility of IHT compared to CAU. Discussion: RCTs on the effectiveness of crisis treatment in psychiatry are scarce and including patients in studies performed in acute psychiatric crisis care is a challenge due to the ethical and practical hurdles. The Zelen design may offer a feasible opportunity to carry out such an RCT. If our study finds that IHT is a safe and cost-effective alternative for CAU it may help support a further decrease of in-patient bed days and may foster the widespread implementation of IHT by mental health care organisations internationally.