The first two cases are reported in which Plesiomonas shigelloides was isolated from patients with mixed aerobic/anaerobic septicaemia originating from the biliary tree. The first patient who was previously well survived after removal of a gangrenous gallbladder. The second patient suffered from an extrahepatic cholangiocarcinoma and died of infection thus highlighting the poor prognostic outcome of P. shigelloides septicaemia in immunocompromised patients. Furthermore these cases demonstrate that P. shigelloides can be isolated from mixed infections and may act synergistically with other bacteria to produce disease.