SUMMARYObjective: One of the risk factor for different psychiatric disorders has been indicated as hypovitaminosis D. The present study aimed to compare 25 (OH) D level between 4 different types of psychiatric disorders (schizophrenia, bipolar disorder, depression and anxiety disorder) and healthy controls, and to assess the risk factors of hypovitaminosis D in psychiatric inpatients. Method: This retrospective study included 974 individuals [depression (n=553), bipolar disorder (n=135), schizophrenia (n=186) and anxiety disorder (n=100)] who received inpatient treatment in psychiatry clinic between 2012 and 2014, and 574 individuals in control group who were not diagnosed with a psychiatric condition. A 25 (OH) D level less than 21 ng/mL was considered to indicate hypovitaminosis D. Results: 25 (OH) D level average of the control group was found to be significantly higher than that of the four psychiatric diagnosis groups (p<0.05). There was no significant difference among 25 (OH) D level of psychiatric diagnosis groups (p<0.05). Comparing 25 (OH) D level among age groups in each study group, it was found that 25 (OH) D level of schizophrenic patients with an age range of 35-54 was found to be significantly lower than that of schizophrenic patients with an age range of 18-34 (p<0.05). 25 (OH) D levels by genders were lower among women in all diagnosis groups (p<0.05), while they were similar for both genders in control group (p>0.05). Logistic regression analysis of the study parameters suggested that the female gender (odds ratio: 3.46; 95% confidence interval: 0.99-1.01), winter and spring seasons (odds ratio: 2.56; 95% confidence interval: 1.69-3.86 and odds ratio: 2.03; 95% confidence interval: 1.33-3.11, respectively) were significant predictors in level of vitamin D in psychiatric inpatients. Conclusions: Hypovitaminosis D is a condition that frequently exists in inpatients in psychiatry clinic suffering from schizophrenia, bipolar disorder, anxiety disorder and d epression. Being a female, winter and spring are the most remarkable risk factors in these patients. Keywords: Hypovitaminosis D, schizophrenia, bipolar disorder, depression, anxiety Sonuç: Psikiyatri kliniğinde yatarak tedavi gören şizofreni, bipolar bozukluk, anksiyete ve depresyon hastalarında vitamin D eksikliği sıklıkla görülen bir durumdur. Bu hastalarda kadın olma ve kış-ilkbahar mevsimleri vitamin D eksikliği için en önemli risk faktörleri olarak belirlenmiştir.