Objectives <p>Examine the responsibility of Vitamin D (VD) deficit as a risk element in the development and severity of oral lichen planus (OLP) considering dietary habits, sex, sun exposure, socioeconomic class and psychological factors.</p> Materials and methods <p>Blood samples from 35 OLP patients and 35 healthy controls were collected for the analysis of serum VD level (SVDL) by ELISA. Vitamin D deficiency was considered when SVDL was ≤ 20 ng/ml. Additionally, a structured questionnaire was used to analyze other possible confounders.</p> Results <p>SVDL were statistically significant greater in the control group than the OLP group (<i>P</i> ≤ 0.001). There was difference between the 3 types of OLP with statistical significance in which the least values for SVDL were in erosive type (<i>P</i> ≤ 0.001). Furthermore, no statistically significant difference was found in SVDL between dysplastic and non-dysplastic lesions. In terms of VD deficiency, a statistically significant distinction was noticed between the two research sets (<i>P</i> ≤ 0.001) and was more pronounced in erosive and atrophic types than reticular types. Depression as well as sun exposure significantly affected number of patients having VD deficiency (<i>P</i> = 0.001, 0.027). Results revealed a statistically significant direct relation between SVDL and the OLP (odds ratio = 1.38; 95%CI = 1.18–1.617).</p> Conclusion <p>VD deficiency plays a vital role in OLP and the development of more severe forms.</p> Clinical relevance <p>It corroborates that VD deficiency is a probable risk factor of OLP and the development of more severe forms considering many confounders.</p>