Prevalence and incidence of dementia were determined for 65-84 year-old persons living in the municipality of Odense and randomly drawn from the Danish Civil Registration System (DCRS). All participants were examined with CAMCOG, the cognitive section of CAMDEX (The Cambridge Examination for Mental Disorders of the Elderly) and the follow-up period was two years. Individualized CAMCOG cut-off scores were determined by multiple linear regression. Possibly demented persons were further examined with the remaining part of CAMDEX and neuropsychological tests. Alzheimer's disease (AD) was diagnosed according to the NINCDS-ADRDA criteria for probable AD, and vascular dementia (VD) and dementias of other types according to the DSM-III-R criteria for dementia. The severity of dementia was determined according to the Clinical Dementia Rating scale. Of the 5,237 persons drawn from the DCRS, 3,346 participated in the prevalence study and 2,452 in the incidence study. The prevalence was 7.1% (66.7% AD, 18.3% VD, and 15.0% dementias of other types). Ninety-six (2.8%) were diagnosed as very mildly demented. The incidence rate was 29.5 new cases per 1,000 person-years and 20.9 for AD. Inclusion of cases with very mild dementia resulted in higher prevalence and incidence rates than generally reported.