The objective of this study was to examine the relationship between multimorbidity and root caries among older American adults. Data from the National Health and Nutrition Examination Survey (NHANES) 2017-2020, a cross-sectional nationally representative survey of civilian noninstitutionalised Americans was used. The analysis included dentate adults aged 50 years and older. The presence of root caries or root restoration was assessed through clinical dental examinations. Multimorbidity was identified by the existence of five common and serious chronic diseases, namely, diabetes, cancer, coronary heart disease, chronic pulmonary disease and stroke. An aggregate variable of these five conditions was created. Logistic regression models were used to assess the association between multimorbidity and root caries (outcome), adjusting for sociodemographic factors and health behaviours. The analysis included 3274 dentate participants (mean age: 63.6 years), 18.2% had root caries, while 14%. had multimorbidity (two or more conditions). The mean number of multimorbidities was 0.65. The count of multimorbidity was significantly associated with root caries, with odds ratios (OR) of 1.26 (95% Confidence Interval (CI): 1.03, 1.52) in a model adjusting for age, gender, ethnicity, income, and education. After additionally adjusting for dental visits and smoking, the association between multimorbidity and root caries lost statistical significance (OR 1.20, 95% CI: 0.97, 1.48). : Individuals with greater numbers of chronic conditions appeared to have higher probabilities of having root caries. However, the significant association was eliminated after accounting for strong behavioural predictors of root caries. The higher level of root caries among those with multimorbidity could be attributed to xerostomia caused by being on multiple medications. The findings highlight the need for interventions to prevent root caries among those with multimorbidity.