Data sources The Longitudinal Health Insurance Database 2010 (LHID2010).Data extraction and synthesis This retrospective cohort study elicited data from the LHID2010 database with a sample of 98,800 patients from 2001 to 2012. To assess the correlation between the exposure (periodontal treatment versus individuals without periodontal disease) and the outcome (pneumonia), Cox proportional-hazards regression analysis was adopted. Propensity score matching was conducted according to age, gender, monthly income, urbanisation and comorbidities to further adjust the comparison group (individuals without periodontal disease) for potential baseline predictor variables.Results Patients who received periodontal treatment had a significantly lower cumulative incidence of pneumonia compared to the individuals in the comparison group throughout the 12-year follow-up period (log-rank test, p <0.001). Further sign-mapping of the data regarding the type of periodontal treatment indicated that scaling (compared to no periodontal treatment) is associated with a significant reduction in the risk of pneumonia (adjusted HR: 0.70; 95%CI: 0.66-0.75). Additionally, intensive periodontal treatment (for example, flap surgery) could lower the pneumonia risk by about 66% compared to no periodontal treatment (adjusted HR: 0.34; 95%CI: 0.19-0.62).Conclusions Conducting periodontal treatment is associated with a reduced risk of pneumonia. When looked at from a healthcare delivery perspective, this nationwide study can present further evidence that providing patients with thorough oral and dental examinations, and following periodontal treatment if necessary, might reduce the incidence of subsequent pneumonia events.