Chronic diseases pose a significant public health challenge, especially among the aging population. Understanding the potential impact of an inflammatory diet on the prevalence of chronic diseases is crucial for effective health interventions.This study assesses the relationship between the Dietary Inflammatory Index (DII) and chronic diseases in older adults.Data from the National Health and Nutrition Examination Surveys (NHANES) were utilized, with the DII calculated from 28 food parameters obtained through 24-hour dietary recalls and food records. Five major chronic diseases, including cardiovascular disease, hypertension, diabetes, COPD, and cancer, were used in the analysis. Logistic multivariable regression was used to determine odds ratios for chronic diseases across DII quartiles and with one unit increment in DII.16,512 adults aged over 60 years were included in the study, with DII scores ranging from - 5.28 to 5.48. In the fourth DII quartile, individuals with one or more chronic diseases were more prevalent than those without. Compared to the first quartile, individuals in the fourth quartile had 28% higher odds of having CVD, 17% higher odds of having diabetes, and 19% higher odds of having hypertension, after adjusting for age, sex, smoking status, drinking status, BMI, ethnicity, poverty, marital status, education, annual family income, and citizenship. Similarly, one unit increase in DII was significantly associated with higher odds of CVD (OR [95%CI] = 1.05[1.02,1.09]) and hypertension (OR [95%CI] = 1.03 [1.00,1.06]). In Model 2, one unit increase in DII was positively associated with the number of chronic diseases (β[95%CI], 0.02[0.01, 0.03], p = 0.003).Higher DII scores were associated with increased odds of cardiovascular disease, diabetes, and hypertension in older adults. Following an anti-inflammatory diet may be beneficial for preventing and treating chronic diseases in an older population.© 2025. The Author(s).