This chapter talks about an 81-year-old, left-handed, Caucasian man who was referred by his internist for evaluation of cognitive change. Initial impression was that of an acute-on-chronic change of cognition and gait, which occurred about a month before the first visit, most likely due to Wernicke's encephalopathy, plus underlying dementia. Potentially contributing factors in the differential diagnosis of the dementia were alcoholism in the past, suspected nutritional insufficiency, possible multi-infarct dementia, and possible Alzheimer's disease. The patient was treated emergently for Wernicke's encephalopathy with intravenous thiamine hydrochloride immediately following the new patient visit. The patient's history suggested both an insidious dementia and an acute change due to some other factor. This case illustrates the importance of obtaining a careful chronology of symptoms in the history, and of entertaining the possibility of both acute and chronic processes.