Abstract: Introduction: Chronic Fatigue Syndrome (CFS) has a complex and multifactorial etiology making treatment and definitive diagnosis, currently made through exclusion, difficult. Current therapies, such as cognitive behaviour therapy and graded exercises, are inadequate and targeted to address symptoms, rather than the underlying disease pathology. Increasing evidence implicates the microbiota of the gut in a number of conditions previously thought distinct from the gastrointestinal system. Previous work with bacteriotherapy in CFS has suggested a link between the condition and the composition and health of the gut microbiota. Here, we review and further examine a larger cohort of CFS patients who had undergone bacteriotherapy for their CFS. Method: A total of 60 patients from the Centre for Digestive Diseases presented with CFS. Of these, 52 patients had concurrent IBS and 4 patients additionally had constipation. All underwent initial transcolonoscopic infusion of 13 non-pathogenic enteric bacteria. 52/60 patients undertook an additional rectal infusion a day later and 3/60 undertook an additional 2 rectal infusions. Results: 35/60 patients who underwent initial bacteriotherapy responded to treatment. 10/15 patients who failed this course were offered a secondary transcolonoscopic infusion followed by a rectal infusion or an oral course of cultured bacteria. Of these 7/10 responded, giving a total of 42/60 (70%) patients who responded to treatment. Contact was achieved with 12 patients after 15-20 year follow-up. Complete resolution of symptoms was maintained in seven of the twelve patients and 5/12 did not experience recurrence for approximately 1.5-3 years post bacteriotherapy. Conclusion: Bacteriotherapy achieves initial success rate of 70% in CFS and a 58% sustained response. Given that manipulation of the colonic microbiota improved CFS symptoms, bacteriotherapy for CFS warrants further investigation and may provide further insight into a possible etiology of CFS.