[The basis of diagnostic and therapeutic decisions (author's transl)].

The recent logical and psychological results of the theories of probability, utility and decision are valid also for medicine. Their principles and methods are briefly described. The review deals with the special conditions for their application in medicine. Diagnostic methods are derived from the principles of exclusion and pattern recognition. Concerning treatment the importance of the so called therapeutic index as a quotient of possible benefit and injury is stressed. From these elements decision rules are developed for the usual clinical situations.