Background Oral health perception is an influential predictor of both current and future health among the elderly. However, limited research has focused on self-rated oral health among older patients attending tertiary dental care. Therefore, this study aimed to explore the potential factors associated with self-rated oral health among elderly patients attending a university dental hospital in Thailand. Methods This telephone-based cross-sectional study was carried out among elderly patients older than 60 years who attended at least one dental visit at the university dental hospital in 2020. Hospital numbers (HN) were used to identify eligible candidates for this study. We calculated the sample size by assuming a finite population of 70,028 elderly patients with valid telephone numbers. The minimum sample required for this study was 398 participants. Trained interviewers conducted telephone calls between July 2021 and January 2022 using the validated modified oral health questionnaire. Self-rated oral health was assessed using a conventionally used global oral health question: “How would you describe your dental health?” with three response options: good, fair, and poor. Descriptive statistics, Fisher’s exact test, and binary logistic regression were performed to analyze the data. Results A total of 836 telephone numbers were called. There were 402 (48.10%) elderly patients who agreed to and completed the telephone interview. Most of the study participants were women (61.4%) between 61–74 years of age (83.1%) with a mean age of 69.18 years. Bivariate analyses showed associations between poor self-rated oral health and lower subjective oral functions: chewing discomfort (p < 0.001) and speaking discomfort (p = 0.013). However, the multivariate regression model indicated a significant association between poor self-rated oral health and chewing discomfort (p < 0.001). Therefore, elderly patients with chewing discomfort were more likely to perceive poor oral health. Conclusions These findings indicate that difficulty chewing could be a potential factor influencing self-rated adverse oral health among older patients attending the university dental hospital. Furthermore, our study adds that the predictive power of a single-item self-measurement supports its value as a standard measure to predict oral health risk in tertiary care institutions, as well as primary care settings and community-based survey research. Therefore, healthcare providers should routinely evaluate self-rated oral health among elderly patients to detect early signs and symptoms of oral health problems, assess the success of dental treatments, and monitor general health and well-being.