Mental illness was recorded in 17% of men and 30% of women at the first examination of a random sample of the population of north Edinburgh consisting of 215 men and 272 women aged 62–90 years. Chronic brain syndrome (CBS) was found in 6% of men and 10.7% of women. CBS severe enough to constitute clinical dementia occurred in 3% of the sample. CBS increased in prevalence with age, particularly in women. Depressive illness was found in 3.7% of men and 6.6% of women. Anxiety states were present in 7% of men and 16.5% of women. Physical health and measurements were recorded in the same random sample in respect of ischaemic heart disease, stroke, blood pressure, chronic bronchitis, respiratory function, visual acuity, audiometry, urinary incontinence and food intake. The physical findings related to CBS were poor vision, poor hearing, urinary incontinence and poor diet. Five years later 113 men and 148 women were re-examined. The annual incidence of CBS was 0.4% in men and 1.4% in women. The annual incidence of depressive illness was 0.8% in both sexes, and of anxiety neurosis was 0.3%. Mortality rates were high in subjects with CBS. All moderate/severe cases of CBS had died by the end of seven years, but 15% of the mild cases were alive after 14 years. Prevalence and incidence of CBS in the study were similar to those reported by other authors. Figures for depressive illness and anxiety neurosis tended to be higher than in other surveys.