Background: Individuals applying for periodontal treatment often have systemic diseases that can adversely affect the periodontal disease course and treatment response. Objectives: To determine the prevalence and types of systemic disease in patients referred for periodontal treatment living in Turkey, and to investigate the association between systemic disease and periodontal status, according to the new classification of periodontal disease (2017). Methods: A total of 800 randomly selected dental files were evaluated among patients who had attended the periodontology department of a university hospital between January 2021 and January 2022. Demographic data (age and gender), self-reported medical history, smoking habits, daily tooth-brushing frequency, periodontal status, and the number of missing teeth were recorded. Full-mouth periodontal examinations were undertaken, and the patients were classified according to the American Association of Periodontology/European Federation of Periodontology 2017 case definitions. Results: The prevalence of systemic disease was 48% among the study participants. Hypertension (HT), diabetes, and cardiovascular diseases (CVD) were the most common systemic diseases identified. Periodontitis was present in 32% of the study population. When periodontitis patients were classified according to their stages; 42% had severe (stageIII\IV) periodontitis, 35% moderate (stage II), and 23% mild (stage I). The prevalence of systemic disease increased according to the severity of periodontal disease (p = 0.000). A significant correlation was also present between the presence of systemic disease and missing teeth (r = 0.120, p = 0.001). On logistic regression analysis, self-reported diabetes (OR = 3.12, 95% CI: 1.90-5.12), HT (OR = 2.49, 95% CI: 1.68-3.68) and CVD (OR = 1.73, 95% CI: 1.01-2.96), age (OR = 1.05, 95% CI: 1.03-1.06), low tooth brushing habits (OR = 2.63, 95% CI: 1.81-3.83) and tobacco use (OR = 1.92, 95% CI: 1.33-2.78) were identified as significant predictors of periodontitis. Conclusions:The present study results suggest an association between self-reported systemic diseases, as well as tobacco use, and periodontal disease severity.