INTRODUCTION: Periodontitis is a common oral disease associated with coronary artery disease (CAD), cerebrovascular disease (CBVD) and type 2 diabetes (T2D). We studied if periodontitis treatment improves clinical outcomes and reduces medical care costs in patients with CAD, CBVD or T2D. METHODS: We used clinic records and claims data from a health care system to identify patients with periodontitis and CAD, CBVD or T2D, and to assess periodontal treatments, hospitalizations, medical costs (total, inpatient, outpatient, pharmacy), glycated hemoglobin, cardiovascular events, and death following concurrent disease diagnoses. We compared clinical outcomes according to receipt of periodontal treatment and/or maintenance care in the follow-up period, and care costs according to treatment status within one year following concurrent disease diagnoses, while adjusting for covariates. The data were analyzed in 2019-21. RESULTS: We identified 9,503 individuals, 4,057 of whom were in the CAD cohort; 3,247 in the CBVD cohort; and 4,879 in the T2D cohort. Patients who were selected and elected to receive treatment and maintenance care were less likely to be hospitalized than untreated individuals (CAD: OR = 0.71 (95% CI: 0.55, 0.92); CBVD: OR = 0.73 (0.56, 0.94); T2D: OR = 0.80 (0.64, 0.99)). Selection to treatment and/or maintenance care was not significantly associated with cardiovascular events, mortality, or glycated hemoglobin change. Total care costs did not differ significantly between treated and untreated groups over 4 years. Treated patients experienced lower inpatient costs but higher pharmacy costs. CONCLUSIONS: Patients with periodontitis and CAD, CBVD or T2D who were selected and elected to undergo periodontal treatment or maintenance care had lower rates of hospitalizations, but did not differ significantly from untreated individuals in terms of clinical outcomes or total medical care costs.