A recent systematic review and meta-analysis has identified an inverse relationship between Helicobacter pylori infection — a common cause of stomach ulcers — and multiple sclerosis (MS). On the basis of data from six observational studies involving 1,902 individuals, the prevalence of H. pylori infection was significantly lower in patients with MS than in controls (pooled OR 0.59). The results suggest that H. pylori affords some protection against the development of MS.