Providers of mental health services need tools to screen for acute psychosis and ultrahigh risk (UHR) for transition to psychosis in help-seeking individuals. In this study, the Eppendorf Schizophrenia Inventory (ESI) was examined as a screening tool and for its ability to correctly predict diagnostic group membership (e.g., help seeking, mild psychiatric complaints, highly symptomatic mood or anxiety disorder, UHR, acute psychosis). Diagnostic evaluation with established instruments was used for diagnosis in 3 research samples. UHR status was assessed with the Structured Interview for Prodromal Symptoms/Scale of Prodromal Symptoms (Miller et al., 1999) and the Bonn Scale for the Assessment of Basic Symptoms Prediction list (Gross, Huber, Klosterkotter, & Linz, 1987; Klosterkotter, Hellmich, Steinmeyer, & Schulze-Lutter, 2001). This study showed that members of different diagnostic groups rate themselves significantly differently on the ESI and its subscales. A new subscale was constructed, the UHR-Psychosis scale, that showed good utility in detecting individuals with interview-diagnosed UHR status and acute psychosis. The scale is also sensitive to the threshold between UHR and acute psychosis. Practical applications of the ESI include use as a diagnostic tool within various settings. (Contains 5 tables and 2 figures.)