Starting from the increasing clinical requirement to make grave decisions (e.g. discontinuation of treatment) during hospitalisation of patients in an apallic syndrome, problems of defining the "apallic syndrome"--compared with the Anglo-American term "persistent vegetative state"--are reviewed. Besides conceptual criticism based on pathogenetic considerations and neuropathological findings the author especially demonstrates the varying inclusion criteria of the clinical syndrome concerning the apallic syndrome as well as the persistent vegetative state. Furthermore attempts to introduce more precisely defined subgroups (e.g. complete apallic syndrome) and new competing terms are shown. Referring to clinical diagnosis the low value of technical studies resulting from a great range of--sometimes controversial--findings contrasts with the high importance of identifying clinically related syndromes. Recent prognostic data that apply to judging the permanence of an apallic syndrome or persistent vegetative state are discussed. From this follows that they are of limited validity for the single patient. Finally it is attempted to work out some implications for clinical proceedings that should enable to meet a situation afflicted with diagnostic and prognostic uncertainties according to the present medical knowledge.