Maladjustment at work is not synonymous with sickness, but when a middle-aged man becomes grossly inefficient in a job at which he has previously excelled, the chances are that he is ill. This paper describes such a case, and the investigations that led to the diagnosis by cortical biopsy of Alzheimer's Disease. So far as is known, this is the first recorded instance in this country of Alzheimer's Disease being diagnosed histologically during life. Apart from its interest as a clinical curiosity, however, this case illustrates some practical problems often arising in the assessment of this type of patient, which can be as difficult and responsible a task as any that the psychiatrist has to undertake.