Background: Chronic urticarial is one of the most common skin diseases, characterized by as a chronic cutaneous condition which severely debilitates patients in several aspects of their everyday life. CU patients suffer from physical, social, and psychological morbidities resulting in a low quality of life. vitamin D is known to exert several actions in the immune system and to influence function and differentiation of mast cells, central role players in the pathogenesis of chronic idiopathic urticarial. Recently, an increasing body of literature showed paradoxical relationships between vitamin D and allergic diseases like food allergy, rhinosinusitis, recurrent wheeze, asthma, atopic dermatitis and eczema. This study was performed to evaluate the relationship between vitamin D levels and susceptibility to chronic idiopathic urticarial.Methods: One hundred and fourteen patients with chronic idiopathic rticarial were recruited in this study along with one hundred and eighty seven sex-matched and age-matched healthy volunteers as the control group. For each patient, urticarial activity score was calculated and autologous serum skin test was done. vitamin D metabolic statue was measured as 25 hydroxyvitamin D using enzyme immunoassay method.Findings: Patients with chronic idiopathic urticarial significantly had lower levels of vitamin D (p<0.01). vitamin D deficiency was significantly associated with increased susceptibility to chronic idiopathic urticarial (p<0.01). There was a significant positive correlation between vitamin D levels and urticarial activity score (r=0.2, p<0.05).Conclusion: This study showed patients with chronic idiopathic rticarial had reduced levels of vitamin D, while vitamin D deficiency could increase susceptibility to chronic idiopathic urticarial.