Presented here is a case of monobacterial peritonitis complicating cholecystitis and caused by an uncommon agent of gastrointestinal infections, Haemophilus parainfluenzae. The pathogenic role of this organism in digestive infections, particularly in those of the biliary tract, has been reported increasingly though sporadically. Indeed, it has been shown to be a coloniser of the gastrointestinal tract, and a recent hypothesis of an ascending route of infection to the biliary tract has been postulated to partly explain its pathogenicity. More frequent identification of Haemophilus parainfluenzae as a causal agent of biliary tract infection would probably be obtained through the use of specific culture media, since its potential implication has been demonstrated.