To consider the possible relationships between vitamin D and algodystrophy syndrome, i.e. complex regional pain syndrome (CRPS), one must understand that bone tissue is a key player in the pathogenetic dynamics of the syndrome. In addition to the results obtained by treatment with drugs whose mechanism of action involves bone tissue as their main target, there is also much evidence supporting the fundamental role that bone has in the onset and maintenance of the disease. Aside from findings arising from diagnostic testing (osteoporosis on standard radiology, hypercaptation on scintigraphy scans, bone oedema on magnetic resonance imaging), epidemiological studies have reported that fracture is the most frequent predisposing event. Consequently, all diseases that lead to an increase in bone fragility and therefore to the incidence of fractures (postmenopausal and senile osteoporosis, osteogenesis imperfecta) are often exacerbated by an increase in the incidence of algodystrophy. As further proof of this pathogenetic link, there are reports showing that osteoporosis is present in patients with CRPS at a significantly higher prevalence than in the general population. Additionally, an animal model that closely reproduces human disease can been obtained by inducing a distal fracture of the tibia. Lastly, it is worth mentioning that an increase in osteoprotegerin (OPG), the molecule involved in the regulation of the RANK/RANKL system, has been implicated in the early stages of the disease.