People living with mental illness report a broad spectrum of nutrition risks, beyond malnutrition, but appropriate and adequately validated nutrition risk screening tools for mental health settings are lacking. This study aimed to develop a nutrition-risk screening tool, the NutriMental Screener, and to perform preliminary feasibility and validity testing. In an international, stakeholder engaging approach, a multifaceted nutrition-risk screening tool for mental health services was developed by means of workshops with international stakeholders and two online surveys. Feasibility of the NutriMental screener was tested as part of a research study in Switzerland with 196 participants, evenly distributed across the three study groups (sixty-seven outpatients and sixty-five inpatients with psychotic or depressive disorders as well as sixty-four controls without mental illness). The NutriMental screener consists of ten items covering different nutritional issues that indicate the need for referral to a dietitian or clinical nutritionist. Almost all patients (94·7 %) reported at least one nutrition risk by means of the NutriMental screener. Prevalence for nutrition risks via NutriMental screener was higher in patients than in controls. Almost every second patient expressed a desire for nutritional support (44·7 %). After further validity testing is completed, there is the potential for the NutriMental Screener to replace malnutrition screening tools as routine screening in various mental health settings aiming to organise nutritional therapy prescriptions in a more targeted and efficient manner.