Primary sclerosing cholangitis is a chronic cholestatic liver disease, whose pathogenesis remains poorly understood. Several studies have shown that PSC patients harbor an impaired gut microbiota. A recent study confirmed that PSC patients displayed a bacterial dysbiosis, characterized by an increased abundance of three different bacteria: Klebsiella pneumoniae, Proteus mirabilis and Enterococcus gallinarum. This study also provides evidence for a possible mechanism of action of these bacteria: notably the formation of pores in gut epithelium leading to an increased gut permeability and the induction of liver inflammation characterized by an increased proportion of T helper 17 (T H 17) cells. For the first time, strong data demonstrate not only an association between gut microbiota and primary sclerosing cholangitis but also a possible causal link.