A retrospective study was conducted on sixteen cases of encephalitis or acute amnesic encephalopathies, only one of which was confirmed by pathological examination, seen over the last fifteen years. The amnesic syndrome was always associated with a very marked anterograde deficiency and the absence of severe disturbances of other higher functions. Its onset was always acute, was secondary to disturbances of consciousness or associated with epilepsy, and in half of the cases presented as a severe infections disorder with high fever. The mood and behavioural disorders, and the temporal epilepsy, were evidenced clinically as a pure or predominant hippocampic lesion. The diversity of the progressive nature of the disorders, and the etiological environmental factors, enable divison into three groups : a group of six cases of postencephalitic Korsakoff's syndrome, probably of herpetic origin, and associated with a stable amnesic syndrome which remained as a sequela ; a group of 5 patients with non-herpetic but probable viral "curable amnesic encephalitis" ; another group of 5 patients with "acute amnesic encephalopathy" with various etiologies and with obvious encephalitic lesions.