Objectives: The goals of this research were to examine whether there is a difference in the level of serum vitamin D concentration between subjects suffering from periodontits and those without pathological changes on the supporting structure of the teeth. The aim was also to investigate whether there are differences in the level of serum vitamin D concentrations in patients with periodontitis with regard to diagnosis, age, sex and smoking. Materials and Methods: Data on age, sex and daily cigarette smoking habits were taken from each subject (n = 40). Blood samples were taken from each of the subjects to determine the blood vitamin D levels. The test group consisted of 20 subjects diagnosed with periodontitis (of which 11 with a moderate and 9 with a severe form of the disease). Their diagnosis was made based on examination, X-ray analysis and measurement of periodontal parameters with a graduated probe. The control group consisted of 20 subjects without pathological changes on the supporting structure of the teeth. Results: The results confirmed a significant difference in the level of serum vitamin D between the control group (healthy subjects) and those diagnosed with periodontitis regardless of the degree. A significant difference in the level of serum vitamin D in subjects with a moderate degree of periodontitis compared to the control group was also confirmed. No significant difference was found between patients with moderate periodontitis and those with a severe form of the disease. Also, no significant influence of sex, smoking and age on the level of vitamin D was found. Thus, the only component with a proven significant influence on vitamin D level is diagnosis. Conclusions: According to the results - a weak negative association of periodontitis with changes in the serum level of vitamin D was found. No correlation of age, sex and smoking on vitamin D level was found.