We report a case of Yersinia enterocolitica septicemia with septic arthritis. Gentamicin administration controlled the septicemia but failed to eradicate the organisms in the joint, in spite of a synovial fluid level four times its minimal inhibitory concentration after four days of therapy. Development of azotemia necessitated change of antibiotic therapy to chloramphenicol, which eradicated the infection. While Y enterocolitica infection in the United States is uncommon, it must be added to the list of organisms causing suppurative arthritis and septicemia in susceptible hosts. Septic arthritis must be distinguished from the much more common reactive theumatic polyarthritis associated with Y enterocolimica infection, for which antibiotic therapy is neither needed nor helpful.