Aim: Vitamin D levels influence the risk of fracture, rickets, osteomalacia, and osteoporosis. Vitamin D protects the body against muscle weakness, helps regulate the heartbeat, strengthens the immune system and thyroid func-tion, and is necessary for normal blood clotting. Vitamin D increases calcium absorption from the digestive tract, helps the accumulation of calcium in the bones and also accelerates the active transport of calcium. Humans obtain vitamin D from exposure to sunlight and from diet. Material and Method: The patients admitted to Suleyman Demirel University Faculty of Medicine Research and Application Hospital during a one-year period were examined to determine 25 OH vitamin D levels. 12,920 male and female patients were included in the study. Statistical analysis was performed with SPSS. Results: There was a significant difference between 25 OH vitamin D levels of pa-tients in the winter season and the spring and summer seasons (<0.05). 25 OH vitamin D levels of men were significantly higher than those of women (<0.05). 25 OH vitamin D levels were low in 72.48% of all patients (<20 ng/ml). The ratio of 25 OH vitamin D levels less than 10 ng/ml was found in 40.92% of the patients. Discussion: When assessing 25 OH vitamin D levels, the season of the year and sex of the patients should be taken into consid-eration.