A unique case of an adult with polymicrobic septic arthritis is described. The patient had the simultaneous isolation of anaerobes and unusual facultative aerobes from two soft tissue abscesses and a noncontiguous joint. It is assumed that the source of the microorganisms was the intestinal tract and that hematogenous dissemination following trauma had occurred. There are only twelve other cases of well-documented acute polymicrobic pyarthrosis in the adult in the English literature.