In 90, 60- to 80-year-old patients with teeth retained in both jaws (mean 20.4 +/- 4.3), a total of 1,092 root surface lesions were recorded. Of these 156 were diagnosed as active caries lesions, whereas 509 were considered inactive, and 427 were filled. About 60% of the elderly had one or more active lesions and 79% had fillings. Seventy percent had more than 8 filled or carious (active or inactive) surfaces. The percentage of carious and filled root surfaces in relation to surfaces at risk demonstrated that the buccal surfaces of lower molars and premolars and upper canines were the most severely affected (RCI = 70%) with fillings predominating on easily accessible surfaces. A constant relationship between active and inactive lesions was found on all other surfaces but third molars and upper incisors. The data suggest that active and inactive root caries lesions must be diagnosed as separate entities if the dynamic nature of root surface caries is to be explored in epidemiological studies and clinical trials.