Objectives: In this study, we aimed to identify the prevalence of discrepancies between clinically assessed periodontal status and self-perceived oral health among Korean adults aged 35 years and older, and examine sociodemographic and health-related factors associated with such discrepancies. Methods: Data from 10,146 adults who participated in the 7th Korea National Health and Nutrition Examination Survey were analyzed using complex sample chi-square tests and multivariate logistic regression. The agreement and discrepancy between clinical periodontal status and self-rated oral health were evaluated using the corresponding clinical and subjective measures. Results: A total of 59.7% of participants exhibited a discrepancy between their clinical periodontal condition and self-perceived oral health. Multivariate analysis indicated that individuals who had received mental health counseling within the past year had a significantly higher likelihood of exhibiting such discrepancies, with an odds ratio of 1.496 (95% confidence interval: 1.072–1.496), compared with those who had not received counseling. Conclusions: A substantial proportion of Korean adults inaccurately perceived their periodontal health. Targeted dental hygiene interventions are essential, particularly for individuals whose mental health issues may increase the risk of oral health status misperceptions.