The concept of delirium has gone through a major transformation in German-speaking psychiatry. In the traditional German-speaking literature, the concept was defined in very broad terms, partially corresponding to our present concept of psychosis. Today, the term is usually interpreted in terms of Bonhoeffer's “acute exogenous reaction types” which are classified under the reversible psychoses with “lowered consciousness”; the reversible (acute) organic psychoses are subdivided into those with and those without disturbance of consciousness.