Gerodontology 2010; doi: 10.1111/j.1741-2358.2010.00383.x The Copenhagen Oral Health Senior Cohort: design, population and dental health Background: In order to study the way old age influence oral health, the Copenhagen Oral Health Senior Cohort (COHS) has been established. Objectives: To describe the design, measurement procedures, and baseline values for COHS including spatial distribution of restorations and dental caries as well as reasons for non-participation. Materials and methods: Seven hundred and eighty-three individuals aged 65 years or older, from a total of 1918 invited elderly people, underwent an interview regarding oral health-related behaviour and a clinical oral examination including measurement of unstimulated whole saliva flow rate. Results: Twelve percent of the COHS was edentulous. The number of dental restorations was higher for women compared to men; however, men had more caries than women. Coronal caries was most frequent on mesial and distal surfaces and on the maxillary incisors and canines; root caries was most frequent on labial surfaces and evenly distributed within the dentition. Only 41% of all invited elderly people accepted the invitation, with old age and poor health being the primary reasons for non-participation. Conclusion: The baseline values for COHS show that a substantial proportion of the participants had retained a natural dentition and that dental caries was prevalent with the anterior maxillary teeth being most affected.