AIM: As data are sparse on the long-term association between periodontal diseases and development of metabolic syndrome (MetS), we investigated their relationship in a Thai cohort over a 10-year observational period. METHODS: Medical records and data on periodontal assessments of 2161 employees of the Electricity Generating Authority of Thailand collected at two time points, 2003 and 2013, were used. Experienced periodontists used standard national and international criteria to define periodontitis and MetS. The impact of baseline periodontitis on subsequent MetS incidence and its components was evaluated using regression analyses. RESULTS: The severity and extent of periodontitis significantly predicted MetS incidence over a decade, with a higher incidence of MetS in individuals with poorer periodontal health. A single percentage increase in the periodontitis extent raised the risk of MetS incidence by 0.4% and the risk of developing individual components of MetS by 0.2%. Independent of periodontal health, age of an individual emerged as a factor impacting MetS development. CONCLUSION: This study highlights the potential effect of the severity and extent of periodontitis on the increased incidence and progression of MetS. Hyperglycaemia and hypertension were the two MetS components most significantly affected by the existence of periodontitis.