Although the Bonn Scale for the Assessment of Basic Symptoms (BSABS) [13] has come into use in several European countries, its diagnostic validity has not yet been sufficiently examined. That is why we have assessed BSABS items on a sample of 243 consecutive admissions to the Department of Psychiatry at the RWTH University, Aachen, and 79 psychologically healthy persons. Then, a cluster analysis was calculated to identify the empirical item-grouping. Five well-interpretable BSABS subsyndromes were found. In addition, uni- and multivariate analyses were computed to evaluate the diagnostic validity of these subsyndromes. We were able to show that every BSABS subsyndrome separates at least schizophrenic, organic mental and affective disorders from personality, neurotic and substance-induced disorders, as well as from psychological health. Furthermore, the subsyndrome "information processing disturbances" differentiates between schizophrenic and organic mental disorders, on the one hand, and affective disorders, on the other, and additionally, the subsyndrome "interpersonal irritation" between schizophrenics and all other persons examined.