The incidence of tooth root caries, the morphology of hard dental tissues and the clinical course of the pathology were studied in 4701 (2526 men and 2175 women) residents of St. Petersburg and the Leningrad Region aged 18 to 88 years, which were divided into age groups according to age periodization of Institute of Age Physiology RAS. The highest prevalence of tooth root caries was revealed in the older age groups making 9.88% in elderly age and 7.4% in old age. In young, 1st and 2nd mature age the tooth root caries was diagnosed relatively rare (in 0.26, 1.35 and 5.02% of cases, respectively). Morphological changes in the tooth root cement that predispose to the development of a carious process were determined. In the first adulthood the caries of the tooth root occurred against the background of gum recession in chronic generalized periodontitis especially diabetes patients. In people of the 2nd mature age, elderly and old age the caries of the tooth root was associated with poor oral hygiene, gingival recession due to periodontal disease, as well as in teeth supporting fixed or removable dentures.