Although easily preventable, Wernicke's encephalopathy (WE) remains a regrettably frequent and largely undiagnosed disorder in alcoholics. Unselected autopsy materials from the United States and Australia give prevalence figures of 2%. In Oslo, Norway, the corresponding figures are somewhat lower, 0.6%-0.8%. Only a fraction of the cases discovered at autopsy have been diagnosed clinically (1%-20%). One third of the cases in postmortem materials have been acute with signs of ongoing thiamine deficiency. In contrast to classical concepts, stupor and coma have been predominating symptoms in such cases. Two thirds have had chronic disease with marked variations in severity of the lesions and corresponding variations in severity of the symptoms, from Korsakoff's psychosis or global dementia in severe cases to a slight memory reduction in mild ones. The wide spectrum of the clinical symptoms has not been fully appreciated and this may in part explain the low level of diagnostic accuracy of the disease.