BACKGROUND: Vitamin D is produced in the skin after sun-light exposure and can also be obtained through food. Vitamin D deficiency has recently been linked with a range of diseases including chronic pain. Observational and circumstantial evidence suggests that there may be a role for vitamin D deficiency in the aetiology of chronic pain conditions. OBJECTIVES: To assess the efficacy and adverse events of vitamin D supplementation in chronic painful conditions. SEARCH STRATEGY: We searched Cochrane CENTRAL, MEDLINE, EMBASE and the Oxford Pain Relief Database for studies to September 2009. This was supplemented by searching the reference lists of retrieved articles, textbooks and reviews. SELECTION CRITERIA: Studies were included if they were randomised double blind trials of vitamin D supplementation compared with placebo or with active comparators for the treatment of chronic pain conditions in adults. DATA COLLECTION AND ANALYSIS: Two review authors independently selected the studies for inclusion, assessed methodological quality, and extracted data. Pooled analysis was not undertaken due to paucity and heterogeneity of data. MAIN RESULTS: Four studies, with a total of 294 participants, were included. The studies were heterogeneous with regard to study quality, the chronic painful conditions that were investigated, and the outcome measures reported. Only one study reported a beneficial effect, the others found no benefit of vitamin D over placebo in treating chronic pain. AUTHORS' CONCLUSIONS: The evidence base for the use of vitamin D for chronic pain in adults is poor at present. This is due to low quality and insufficient randomised controlled trials in this area of research.