Wernicke encephalopathy and Korsakoff psychosis are two facets of the same disease with well-determined cerebral lesions caused by thiamine deficiency. The disease occurs mainly in alcoholics, but other conditions (malabsorption or severe malnutrition) also predispose to the risk of Wernicke-Korsakoff syndrome. The incidence in Denmark is unknown. In the period 1.1.1979-31.12.1988, 24 patients (18 men and six women) were discharged from Rigshospitalet with the diagnosis Wernicke encephalopathy or Korsakoff psychosis. This represents about 0.05% of all admissions in the period. Eighteen out of the 24 cases (75%) were admitted in the past three years (1986-88). The mean age was 55 years. Twenty patients admitted alcohol abuse. The presenting symptoms and the patients' complaints showed great variety and were often related to other alcoholic complications, which could mask the disease. The classic symptom combination: eye movement abnormalities- ataxia and disorders of consciousness were found in seven patients (29%). Sixteen patients had disorders of consciousness or orientation. All the patients were treated with thiamine. The eye-movement disorder has recovered in eight out of ten known cases (80%), nystagmus--in six out of seven cases (86%) while ataxia, disorders of orientation and confabulation recovered in about 50% of cases. The average duration of hospitalisation was 50 days. Altogether nine patients died during the observation period. The condition is most probably underdiagnosed and the traditional diagnostic criteria are considered too rigid. The diagnosis should be considered in alcoholics who present even only one of the classical symptoms and in patients with alcohol dementia. Thiamine should be given on wide indications.