The prevalence of root surface caries was estimated in 83 patients surgically treated for periodontal disease and some relating factors were analyzed. The overall root caries index (RCI) was 6.28%. Anterior teeth in the mandible were significantly less affected than other groups of teeth. Root surfaces, divided into subgroups according to surgical treatment and length of exposure, showed no significant differences in RCI. No correlation was found between DFS-index and RCI. RCI increased with age. Concomitantly in older people more time had elapsed between the periodontal treatment and the present clinical examination. Salivary S. mutans counts and a combination of higher salivary S. mutans and lactobacilli counts were good indicators for the presence of root surface caries.