Aim: The aim of the present study is to compare the subgingival temperature in smokers and non smokers, having adult periodontitis. Materials and methods: Thirty-three patients (16 smokers and 17 non smokers) having adult periodontitis were selected for the purpose of this study. A modified digital thermometer was used for recording the subgingival temperature. Other clinical parameters like probing pocket depth, gingival bleeding index and plaque index were also recorded. Only the upper anterior teeth were included in the study. Results: The subgingival temperature in smokers was found to be considerably less than that of nonsmokers. The subgingival temperature increased with increase in probing pocket depth. The gingival bleeding index in smokers was lower than that of nonsmokers. Discussion: The decreased subgingival temperature in smokers is due to the decrease in cellular activity in smokers, thereby generating less heat. As the cellular and molecular activity increases with increase in probing pocket depth in both the smokers and non smokers, the subgingival temperature was found to increase with increase in probing pocket depth. The vaso constrictive action of nicotine in the peripheral circulation in smokers causes a decrease in gingival bleeding in smokers when compared to non smokers. Conclusion: This study shows that the subgingival temperature in smokers is lower than that of nonsmokers. Also it can be said that subgingival temperature measurements, can be successfully used as a chair side diagnostic technique to measure the presence of disease, as it reflects the clinical status of the periodontium.