BACKGROUND: Use of decision aids in mental health care is increasing and will also be introduced in the Dutch mental healthcare system. We describe the context of this development and discuss how decision aids could facilitate evidence-based psychiatry. AIM: To describe the development of the decision aid TReatment E-Assist (TREAT) in the Dutch mental healthcare system that aims to optimize treatment of people with a psychotic illness. METHOD: We describe how the TREAT application works and discuss its potential contribution to the treatment of people with a psychotic illness. RESULTS: In a pilot study TREAT was judged as user friendly and useful. TREAT seemed to increase the integration of ROM-results in treatment and the advice offered ne...