Science in medicine is never a self-fulfilling goal but always serves the purpose to provide the best medical care in a unique clinical situation. Coming to a rational therapeutic decision requires a diagnosis in the sense of allowing and legitimizing an action-oriented individual statement. The diagnosis, however, cannot be reduced to a process of abstraction and formalization, but it rather consists of the ability to allocate general designations of illness to an individual patient. This requires a person-oriented, not necessarily strictly formal knowledge. Inasmuch as guidelines should not become imperative instructions, the individual medical judgment should remain an indispensable focus of the identity of the medical profession.