The goal of the Amenability Psychotherapy Project (APP) is to create a clinician-report tool that is capable of detecting patients with indications for psychotherapy based on efficacy evidence from the first visit. This easy-to-learn tool would be useful in daily clinical practice in mental health services because it is manageable, easy and quick to fill in, and clearly reliable and valid. This tool would not be confined to the boundaries of categorical diagnosis, but would also predict the effect of psychotherapy to reduce symptoms and dysfunctional relationships aside from the severity of the initial clinical picture. In an early phase of the project, we conducted a comprehensive literature search to identify and select patient centred factors that have strong scientific evidence to predict psychotherapy outcomes; the result is a Likert-based evaluation tool, the APP Scale, composed of 22 items. The three objectives of this study are: 1) to evaluate inter-rater reliability using Cronbach’s alpha; 2) to apply the APP Scale to a sample of 100 unselected consecutive psychiatric outpatients from the Psychiatric and Psychotherapy Unit (S.C. Psychiatry 4, A.O. Niguarda Ca’ Granda) to assess the validity of the APP Scale in clinical practice; 3) to verify the internal validity of the Scale with principal component analysis (PCA). The APP Scale was found to be a reliable and valid tool: it is easy and quick to fill in, and acceptable for both the patient and clinician. As for internal validity, the PCA results show a three-factor solution, which explains 62.047% of variance. We named the three components “ego strength”, “ psychological expression” and “illness”. All of the items seem to be maintained.