You visit a 67-year-old man at home who is reported as being confused. His wife is distressed because he repeatedly asks her to swat the flies from the ceiling, when she can see nothing there. He has been in bed for 3 days with a ‘cold’. He frequently gets up and wanders around without knowing where he is going. His wife says on one occasion he burst out laughing without any reason that she could discern. At other times he seems bewildered. She describes that he becomes more confused in the evening and at night, and has urinated in the cupboard. He has no diarrhoea. A week ago he was well and able to do gardening. He has not been confused until recently. On questioning his wife says that while he occasionally forgets the names of village acquaintances, his memory has otherwise been fine. He is not a large user of alcohol and drinks only a small bottle of beer or a sherry once per week. His wife has remained well throughout.