The hypothesis that head injuries and surgical anaesthetics might contribute to the risk of age-related cognitive impairment was tested in a prospective study of 103 patients with dementia of Alzheimer type (DAT), and 26 patients with multi-infarct dementia (MID). 90 age-matched demented community controls were studied in a comparison group. A family history (dementia in a first-degree relative) was found significantly more commonly in DAT (31.6%) than in MID (11.5%) or controls (8.9%). Head injuries were more common in demented patients (11.6%) than in controls (5.5%). The highest incidence (13.6%) was found in the group with DAT though the difference was not significant. No difference was found in the incidence of prior surgical anaesthetics amongst the three groups. The results are briefly discussed.