Aim of the work: This study aimed to investigate serum levels of vitamin D in patients with Behc¸ et’s disease (BD) and to evaluate their relationship to disease activity as well as different disease measures. Patients and methods: Forty-two patients with BD were enrolled into this study. These patients were subjected to detailed history taking, thorough clinical examination including assessment of disease activity according to Behc¸ et’s Disease Current Activity Form (BDCAF) score and performed laboratory investigations including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), serum calcium, serum phosphorus and serum alkaline phosphatase. Serum 25-hydroxyvitamin D (vitamin D) levels were determined using Enzyme-Linked-Immunosorbent Assay (ELISA). A control group of 41 age and sex matched healthy controls was also included. Results: The mean level of 25-hydroxyvitamin D (30.65 ± 12.87 ng/ml) was significantly decreased in BD patients compared to the controls (37.98± 15.76 ng/ml) (p= 0.02). Significant negative correlations of serum vitamin D levels with patients’ ages (p= 0.03), ESR (p< 0.001), CRP (p< 0.001) and BDCAF (p= 0.003) were found; whereas, there was no significant correlation with disease duration (p= 0.6). In multivariate regression analysis age (p= 0.02), colchicine therapy (0.008), ESR (0.02) and CRP (0.03) were found to be the independent effectors on vitamin D serum levels. Conclusion: Serum levels of vitamin D were significantly lower in BD patients compared to controls. Associations were found between vitamin D levels and age, BDCAF as well as ESR and CRP in BD patients. Low vitamin D may predispose BD patients to active disease, especially in older subjects.