Joaquim CR, et al. - This research was designed to compare the combined and individual impacts of diabetes mellitus (DM) and smoking on the levels and prevalence of key subgingival periodontal pathogens among patients with chronic periodontitis. No significant difference was found regarding the subgingival levels and prevalence of the bacterial species in subjects with chronic periodontitis presenting DM, smokers or smokers with DM. Moreover, in patients with chronic periodontitis, DM and smoking, jointly and individually, did not considerably influence the subgingival levels of target periodontal pathogens.