Diabetes is associated with a high prevalence of periodontal disease, but little is known about the effects of periodontal disease on incident diabetes. In total, 5848 non-diabetic individuals aged 30-59 yrs who completed a health examination were analyzed in this study. They were divided into three categories: no pathological pockets, moderate periodontitis, or severe periodontitis. Incident diabetes was defined as newly diagnosed cases with fasting plasma glucose > 125 mg/dL. Cox proportional hazards models estimated the effect of periodontitis on incident diabetes during a seven-year follow-up period. Moderate and severe periodontitis was significantly associated with an increased risk of diabetes in unadjusted analyses, but the magnitude of the association decreased after full adjustment [hazard ratio (HR) = 1.00, 95% confidence interval (95% CI) = 0.77-1.30 and HR = 1.28, 95% CI = 0.89-1.86, respectively]. Our findings do not indicate an apparent association between periodontitis and incident diabetes, although there was a tendency for increased risk.