Following a historical review and critical appraisal of the literature (problems of definition, selection, frequency, etiology, relation and classification) clinical findings from a series of retrospective and prospective studies (four samples with altogether 47 epileptic patients) are presented and discussed, as well as the results of EEG, CT and other relevant investigations. (1) ‘Schizophrenia-like’ interictal (periictal) psychoses in the epilepsies, which are not rare, appear to be true schizophreniform (= schizophrenic-accentuated) syndromes in a setting of ‘clear’ consciousness. There is no case of alternative psychosis and EEG ‘forced normalization’. (2) Between schizophrenic-accentuated syndromes associated with regularly symptomatic epilepsies and genuine (endogeneous) schizophrenias, there are quantitative but no qualitative differences. Often there is a congruence and no possibility of differentiating in the transverse study. This is also true both for the affective and the cognitive disturbances (‘structure of consciousness’); the latter are not suitable for separating the psychopathological syndromes of epilepsies. A discrimination between ‘genuine’ and ‘symptomatic’ schizophrenia is no longer meaningful. (3) A true (hereditary) coincidence of (genuine) epilepsy and schizophrenia occurs obviously very seldom. (4) Numerous findings are presented, concerning the conditions in which schizophrenic-accentuated syndromes appear. The following relevant factors are discussed: hereditary, latency, duration of illness, type and frequency of seizures, type and localization of EEG foci, type, extent and topography of brain lesions, quantity and quality of psychopathological findings as well as ‘organic’ psychosyndromes. The possible triggering of psychoses by psychosocial factors, low intelligence, chronic folate deficiency and other specific risk factors and the role of neurotransmitter disorders (GABA hypotheses) are discussed. Finally proposals are made concerning prevention and therapy. Especially often diagnosed non-alternative schizophrenic syndromes in epileptic patients must be controlled by blood levels of antiepileptics. There is a transitional rank, constituted by defined determinants between the poles epilepsy and schizophrenia or a converging course of those syndromes. The results should lead to more frequent EEG and CT eventual magnetic resonance imaging or positron emission tomography-investigations in schizophrenic patients.