The purpose of this study was to compare subgingival temperature in a group of smokers to that of a group of non-smokers with similar levels of periodontal disease. 40 adult subjects, 20 cigarette smokers and 20 non-smokers with evidence of adult periodontitis were examined. Subgingival temperature was measured at 6 sites around each of 4 maxillary anterior teeth. Probing depth, and the presence or absence of bleeding was also recorded. In addition, the sublingual temperature was recorded. All sites were classified as diseased or healthy. Healthy sites did not bleed and had a probing depth of < or = 4 mm, diseased sites were any site which had a probing depth > or = 5 mm, or which bled on probing. Mean sublingual and site temperatures were calculated for smokers and non-smokers. Mean temperature differentials (delta T) between the sublingual temperature and the site temperature were calculated for each site. Smokers had a warmer mean sublingual temperature than non-smokers. A significant difference in subgingival site temperature was demonstrated between the smokers and non-smokers, with the mean site temperature being 0.4 degree C warmer in smokers (p < 0.01). When healthy or diseased sites were compared between smokers and non-smokers, smokers also had warmer mean site temperatures than non-smokers for both healthy and diseased sites (p < 0.01). When the mean temperature differentials (delta T) between healthy and diseased sites were compared across each group, significant differences were also found. For healthy sites, the smokers had a mean delta T 0.2 degree C lower (p < 0.01) than the non-smokers, representing warmer sites. In diseased sites however, delta T was 0.3 degree C higher (p < 0.01) in smokers, representing cooler sites.