A 37-year-old man presented with an acute amnestic syndrome of Korsakoff's type and an upper brain-stem oculomotor syndrome. After a moderate improvement with steroid therapy, he developed progressive behavioural changes due to a frontal lobe syndrome, in addition to motor and visual impairment. Memory performance was investigated on several occasions during an 11-year follow-up. Diagnosis of laboratory-supported definite multiple sclerosis was established and magnetic resonance imaging showed disseminated white matter lesions, especially in both medial temporal lobes. No other cause than multiple sclerosis was found for the amnestic syndrome. Among the rare cases of Korsakoff's syndrome in the course of multiple sclerosis, this is to our knowledge the first case in which a memory deficit was the initial manifestation of the disease.