Introduction: Fibromyalgia (FM) is a disorder characterized by chronic and widespread musculoskeletal pain, often associated with debilitating fatigue, unrefreshing sleep, lack of recognition, depression and anxiety due to an innocuous stimulus that is usually not painful) and hyperalgesia (ie, exaggerated pain caused by a noxious stimulus)(1). Globally, the mean prevalence of FM is 4.2% in women and 1.4% in men, with a female/male ratio of 3:1. Vitamin D is an important regulator of the immune system, acting as an active cofactor in the incidence of autoimmune disorders such as multiple sclerosis, rheumatoid arthritis, insulin-dependent diabetes mellitus, and irritable bowel syndrome. Vitamin D deficiency is defined as a serum level of 25-hydroxy vitamin D that is less than 25 ng/ml (50 nmol/ml)(3). There is no consensus on the association between vitamin D and FM. Several studies have ...