OBJECTIVES:  In order to aid clinicians in the early identification of patients with major depressive disorder (MDD) in need of highly specialized care, we developed the Decision Tool Unipolar Depression (DTUD). The aim of this study was to assess the feasibility, reliability and validity of the DTUD in patients with a primary diagnosis of MDD. METHODS:  A total of 243 outpatients who were referred for treatment to a general psychiatric or highly specialized treatment centre were studied. The duration of completion and content clarity of the DTUD were used as indicators of feasibility. Inter-rater reliability was assessed using pairs of independent ratings (n=54). To assess convergent validity, the Maudsley Staging Method (MSM), the Dutch Measure for quantification of Treatment Resistance in Depression (DM-TRD) and the five-level EuroQol five-dimensional questionnaire (EQ-5D-5L) were administered. A receiver operator characteristic (ROC) curve was constructed to assess the criterion validity. RESULTS:  The average completion time of the DTUD was 4.5 min (SD=2.7), and the content of the total set of items was judged as clear in 94.7% of all evaluations. Krippendorff’s alpha values of the individual items and total score ranged from 0.686 to 0.913, indicating acceptable inter-rater reliability. The pattern of correlations between the total DTUD score and total MSM (r_s=0.466, P=0.000), DM-TRD (r_s=0.525, P=0.000), and EQ-5D-5L (-0.649, P=0.000) scores supported convergent validity. A maximum Youden index (J=0.494) was obtained at a cut-off score of ≥5. This cut-off score revealed a sensitivity of 0.67 (95% CI 0.52–0.79) and a specificity of 0.83 (95% CI 0.73–0.90). CONCLUSIONS:  The DTUD provides an easily used, reliable and sufficiently valid tool for the identification of patients with MDD in need of highly specialized care. Its use in clinical practice will guide in the assignment of patients with MDD to the most appropriate treatment setting.