The prevelance of mental diseases and abnormalities in a representative, systematic sample of 70-year-olds in Gothenburg, Sweden, is presented. Out of 460 selected subjects, 392 (85.2%) took part and the responders and non-responders were similar in several respects. A case was defined by cut-off points on symptom and/or sign rating scales and diagnoses were defined operationally but as closely as possible to the ICD-classification. The total psychiatric morbidity, excluding personality deviations, was 16.9% in men and 26.1% in women, and excluding also mild neuroses 12.7% in men and 15.5% in women. The prevalence of psychoses was 3.0% in men and 3.5% in women, of neuroses of moderate-severe degree 6.6% in men and 11.5% in women, of neuroses of mild degree 4.2% in men and 10.6% in women, of alcoholism 3.0% in men and 0.0% in women and of oligophrenia 0.0% in men and 0.4% in women. The prevalence of demential syndromes of a psychotic degree was 2.4% in men and 1.3% in women, of a neurotic degree 4.2% in men and 1.8% in women and the total prevalence of demential syndromes was thus 6.6% in men and 3.1% in women. Indications of previous alcohol problems and no or a low current consumption of alcohol were noted among 18.1% of the men.