In the international research on schizophrenia, the early detection and intervention already in the initial prodromal phase prior to the first psychotic manifestation has become one of the main aims in recent years. Therefore, in the present study, the diagnostic efficiency of initial prodromal symptoms was examined prospectively for the first time ever. At index-examination, patients were examined with the 'Bonn Scale for the Assessment of Basic Symptoms--BSABS' and the ninth version of the 'Present State Examination--PSE 9'. At that time, none of the 160 patients had shown psychotic symptoms, but in 110 of the cases prodromal symptoms were found. At the reexamination that took place in average 9.6 years later, patients were explored with regard to a meantime transition to a first psychotic episode applying the same instruments as at index-examination. 79 of the 160 patients (49.38%) had developed a schizophrenic disorder according to DSM-IV-criteria in the catamnestic interval. In general, the 66 assessed prodromal symptoms exhibited a high sensitivity (.98), a high negative predictive power (.96) and a low percentage of false-negative predictions (1.3%), but lower values of specificity (.59) and positive predictive power (.70) as well as a higher percentage of false-positive predictions (20.6%). However, for a subset of mainly cognitive prodromal symptoms with a sensitivity sufficient for diagnostic criteria, high specificities (.85-.91) and positive predictive powers (.71-.91) as well as satisfactory percentages of false-positive predictions (7.5%-1.9%), and good classification rates (81.25%) were found. The results show that the applied conceptualization of prodromal symptoms that originates in the German psychopathological tradition is indeed useful for an early detection of psychoses. By assessing those prodromal symptoms, which were proven to be highly predictive, a diagnosis of schizophrenic disorders already seems possible in the initial prodrome. Thus in future, an early intervention related to them might enable a prevention of first psychotic episodes.