The study examined the feasibility of differentiating frontotemporal dementia from Alzheimer's disease on the basis of retrospective historical information obtained from relatives of patients. A structured questionnaire was devised of patients' symptoms, with emphasis on those cognitive and neuropsychiatric features found in earlier prospective clinical studies to distinguish the two conditions. The questionnaire was given to close relatives of deceased patients in whom the diagnosis of non-Alzheimer's frontotemporal degeneration of Alzheimer's disease had been verified at necropsy. The interviewer had no previous contact or knowledge of those patients, nor clinical experience of patients with frontotemporal dementia. The questionnaire elicited a distinct profile of responses for the two diagnostic groups with emphasis on early personality change, unconcern, and socially inappropriate behaviour in frontotemporal dementia and disturbance in memory and topographical orientation prominent in patients with Alzheimer's disease. A scoring system separated out individual patients with frontotemporal dementia from those with Alzheimer's disease. It is concluded that it is possible to obtain useful information about the precise pattern of dementia from informants even many years after the patient's death. The questionnaire provides the foundation of a diagnostic instrument for use in family history studies of dementia.