Numerous cross-sectional epidemiological studies suggest that obesity is associated with periodontal disease. This longitudinal study tested whether body mass index (BMI) was related to the development of periodontal disease in a sample of employed Japanese participants. Data are from the statutory medical checkups routinely collected for employees in and around Nagoya, Japan. The authors tested the relationship between BMI at baseline and the 5-year incidence of periodontal disease in a sample of 2787 males and 803 females. The hazard ratios for developing periodontal disease after 5 years were 1.30 (P < .001) and 1.44 (P = .072) in men and 1.70 (P < .01) and 3.24 (P < .05) in women for those with BMIs of 25-30 and ≥ 30, respectively, compared to those with BMI < 22, after adjusting for age, smoking status, and clinical history of diabetes mellitus. These findings demonstrate a dose-response relationship between BMI and the development of periodontal disease in a population of Japanese individuals.