Vitamin D plays an important role in the immune system; decreased serum vitamin D concentrations have been linked to dysregulated immune function. Low vitamin D status is probably associated with chronic spontaneous urticaria (CSU). We evaluated the prevalence of low vitamin D status, and the clinical response and quality of life following vitamin D supplementation, in a prospective case-control study with 60 CSU patients and 40 healthy individuals. Serum 25-hydroxy vitamin D (25(OH)D) concentrations were measured at baseline and after 6 weeks. For patients with 25(OH)D concentrations – 30 ng/ml, treatment included 20,000 IU/day of ergocalciferol (vitamin D2) and non-sedative antihistamine drugs for 6 weeks. Urticaria symptom severity and quality of life