The clinical course of six alcoholics with Korsakoff's psyter shunt operation. The initial clinical state as well as the symptom improvement showed important similarities between the Korsakoff group and the hydrocephalic dementia group, who improved after shunt operation. Fantastic confabulation and appraxia were only observed in the hydrocephalic dementia group. Psychometrically, both groups showed a similar degree of improvement of the initially impaired verbal memory while only the hydrocephalic dementia group showed impairment of spatial abilities indicating a constructional apraxia. It is suggested that the similarities of the two conditions are related to dysfunction of diencephalic and temporal-limbic structures. The constructional and general apraxia as well as the fantastic confabulation in hydrocephalic dementia indicate a cortical, especially frontal cortical, dysfunction in this disorder.