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 dis-ease 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), serumcalcium, serumphosphorus and serumalkaline phosphatase. Serum25-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 correla-tion with disease duration (p= 0.6). In multivariate regression analysis age (p= 0.02), colchicine