Objectives. Physical activity has been shown to have a protective relationship with several chronic diseases. Recently, physical activity was also found to reduce the risk of periodontitis in a study in mate health professionals. However, the relationship between physical activity and periodontitis in a diverse group of individuals is not thoroughly examined. The purpose of this study was to examine if there is an association between sustained physical activity and periodontitis in a subset of the third national health and nutrition examination survey (NHANES III). Methods. NHANES III participants 18 years of age or older who had had a periodontal examination and reported to have a similar physical activity (or inactivity) level for 10 years or longer were selected (n=2521). Multivariable Logistic regression analysis was used to estimate the association between physical activity and periodontitis. The analysis was adjusted for: age, gender, race, education, smoking, body mass index, poverty index, vitamin use, healthy eating index, time since Last dental visit, gingival bleeding, and dental calculus. Results. Engaging in the recommended level of physical activity was significantly associated with lower periodontitis prevalence (OR=0.58, 95% Cl, 0.35-0.96). Smoking, however, was found to modify this relationship. The association was strong and significant among never (OR=0.46, 95% Cl, 0.23-0.93) and former smokers (OR= 0.26,95%Cl: 0.09-0.72), but not among current smokers (OR= 1.10, 95%Cl: 0.48-2.53). Conclusions. These results suggest that engaging in the recommended level of exercise is associated with tower periodontitis prevalence, especially among never and former smokers. (c) 2005 Elsevier Ltd. All rights reserved.