The cardiometabolic index (CMI) is a new predictor of obesity-related diseases, but its link to periodontitis is under-researched. This study aims to examine the potential association between the CMI and periodontitis. We conducted a cross-sectional study using the National Health and Nutrition Examination Survey (NHANES) database (2009-2014) to examine the potential association between CMI and periodontitis. The study utilized a weighted multivariate logistic model to assess the association between TG, HDL-C, TG/HDL-C, obesity indices (BMI, WC, WHtR, CMI), and periodontitis, employing the area under the receiver operating characteristic curves (ROC) to estimate areas under the curve (AUC). Furthermore, generalized smooth curve fitting was conducted to examine the relationship between CMI and periodontitis. Finally, the study incorporated subgroup analysis and interaction tests to examine consistency across different populations. TG/HDL-C, WHtR, and CMI were positively associated with periodontitis in the fully adjusted classification model. It was observed that for each unit increase in CMI, there was a corresponding 17.8% increase in the prevalence of periodontitis [1.178 (1.049, 1.322) 0.00562] and 18.7% increase in the prevalence of moderate/severe [1.187 (1.057, 1.334) 0.00376] in the fully adjusted model. When CMI was used as a categorical variable, the adjusted OR for periodontitis prevalence increased significantly with increasing CMI after adjusting for all potential covariates (T3 vs. T1: OR, 1.28 [1.06, 1.55], p < 0.05). The ROC analysis indicated that a larger area under the curve was found in the CMI [0.554 (0.538-0.570)] than in the WC [0.544 (0.528-0.560)] and WHtR [0.544 (0.528-0.561)]. Nonetheless, the discrepancy observed did not reach statistical significance (all p > 0.05). Further generalized smooth curve fitting and threshold effect models indicated a positive linear correlation between CMI and periodontitis. Moreover, there is no interactive association between TG/HDL-C, WHtR, CMI, and periodontitis. This cross-sectional study revealed a positive relationship between CMI and periodontitis. Further prospective studies are warranted to validate our findings.