<p class="p p-first-last" id="__p2">Clinical and microbiological characteristics of patients with <em>Bacteroides </em>prosthetic joint infection (PJI) have not been well described in the literature. The aim of this retrospective cohort study was to assess the outcome of patients with <em>Bacteroides </em>PJI and to review risk factors associated with failure of therapy. Between 1/1969 and 12/2012, 20 episodes of<em> Bacteroides</em> PJI in 17 patients were identified at our institution. The mean age of the patients in this cohort at the time of diagnosis was 55.6 years; 59% (n=10) had knee involvement. Twenty four percent (n=4) had diabetes mellitus, and 24% had a history of either gastrointestinal (GI) or genitourinary (GU) pathology prior to the diagnosis of PJI. Thirty five percent (n=6) were immunosuppressed. The initial medical/surgical strategy was resection arthroplasty (n=9, 50%) or debridement and implant retention (n=5, 28%). Thirty seven percent (n=7) were treated with metronidazole. Eighty percent (n=4) of patients that failed therapy had undergone debridement and retention of their prosthesis, as compared to none of those treated with resection arthroplasty. Seventy percent (n=14) of patient episodes were infection free at their last date of follow up. In conclusion, a significant proportion of patients with <em>Bacteroides </em>PJI are immunosuppressed and have an underlying GI or GU tract pathology. Retention and debridement of the prosthesis is associated with a higher risk of treatment failure.</p>