Objective: To assess the prevalence of comorbidities and periodontal diseases severity in dental patients and to determine the socio-demographic, behavioral, and comorbidity-related predictors of periodontal diseases severity. Material and methods: This retrospective study sample consisted of 2458 patients who referred to faculty dentistry clinic. Socio-demographic, behavioral, and comorbidity characteristics of study participants were collected using hospital database and self-reported questionnaire. Descriptive, bivariate, and multivariate analyses were used to analyze study data. Results: Of these patients, 55.2% had mild-to-moderate periodontitis and 44.8% had severe periodontitis. The severity of periodontal disease was significantly associated with the presence of comorbidity, the number of comorbidities, age, gender, income level, smoking, and alcohol consumption. Patients with severe periodontitis were more likely being a current smoker, to report drinking alcohol sometimes or every day, to be a male, to have a pulmonary disease, to have an endocrinological and metabolic disorder, to have a cardiovascular disorder and to have a neurological disorder than those with mild/moderate periodontitis. Having a hematological disorder, having a muscle, skeletal and connective tissue disorder, to be a current smoker and lower age were found to be predictors of moderate periodontitis whereas being a female and lower number of comorbidities were predictors of mild periodontitis. Conclusions: The severity of periodontitis was associated with socio-demographic, behavioral, and comorbidity characteristics of periodontal patients.