BACKGROUND: Limited information is available about patient knowledge and perceptions of periodontal diseases. In this observational, survey-based study, the authors investigated patients' understanding of periodontal diseases and their experience after periodontal therapy using self-reported oral health-related quality of life. METHODS: Patients receiving oral health care at the College of Dentistry, University of Oklahoma, were recruited and surveyed about topics related to general knowledge, etiopathogenesis, treatment outcomes, level of treatment satisfaction, and oral health-related quality of life in the context of periodontal diseases. The collected data were analyzed using descriptive and bivariate statistical methods. RESULTS: A total of 190 surveys were collected. The results showed that 19.6% of patients did not know whether they had received a diagnosis of periodontitis and 13.7% were unaware whether they had undergone any treatment for it. Patients who reported having periodontitis had a better understanding of what a periodontal pocket was than healthy patients (79% vs 48%) and agreed smoking tobacco products could worsen the condition (92% vs 69%). Patients who had received a diagnosis of periodontal disease were more concerned about their teeth (eg, esthetics, tooth loss, function, and discomfort) than healthy patients (84.3% vs 58.9%). Lastly, a strong association was found between patients' total knowledge scores and positive attitude toward their dental health and periodontal therapy. CONCLUSIONS: Patients generally have a limited understanding of their periodontitis diagnosis and treatment. However, those requiring advanced treatment had a better understanding of their condition compared with patients not treated for periodontitis. PRACTICAL IMPLICATIONS: Clinicians will dedicate more time to patient education about periodontal diseases.