Over the last dozen years, increasingly powerful DNA sequencing methods have allowed characterization of the microbes residing on and in humans in much greater detail than ever possible before. Abnormalities present in the gut microbiome--those microbial communities residing in our intestines--have now been observed in a number of diseases. One such illness is Myalgic Encephalomyelitis (ME), also known as Chronic Fatigue Syndrome (CFS). CFS was a name coined by the US Centers for Disease Control (CDC) in 1988, and reviled by patients for the resultant trivializing of this serious illness. Recently, the US National Academy of Medicine (NAM) recommended a new name: Systemic Exertion Intolerance Disease, though this name is not yet widely used. In ME, as in other diseases, the diversity of the bacterial species in the gut microbiome is lower than in healthy individuals. Furthermore, the abundances of different bacterial residents of the gut, which influence health both favourably and negatively, differ between ME patients and healthy controls. Bacteria translocate into the blood in greater amount in ME, leading to inflammation. Dysbiosis in the gut likely contributes to symptoms in this life-limiting disease.