Retrograde enteroscopy involves an examination of the distal ileum at colonoscopy using a standard colonoscope, a small bowel enteroscope, or a small endoscope passed through the instrument channel of a specially designed therapeutic colonoscope. The ileocecal valve is intubated 72-79% of the time the routine colonoscopy, the length of the terminal ileum is considered variable, and the diagnostic yield has been reported to be up 2.7%. In a study in which push enteroscopy from above was combined with retrograde ileoscopy in the investigation of obscure gastrointestinal bleeding and IDA, ileoscopy provided a diagnosis in 1.3% of cases, the average length of ileum examined was 60 cm. In the only report on the use of a second of 3.4 mm diameter endoscope passed through the instrument channel of a colonoscope, the procedure was complicated by technical problems, and adequate visualization was achieved in only 70%, abnormalities were observed in 20%. However, dedicated retrograde enteroscopy seems to have a low yield and should be reserved for cases where other evidence indicates a potential source of blood loss in the terminal ileum.