There are few published reports of Trichuris dysentery syndrome (TDS) in children. The disease has not been reported in adults. To report the clinical, colonoscopic, and histologic findings of TDS in adults in an endemic area. Case series. Tertiary gastroenterology center. Eighty-four consecutive adult patients with chronic iron deficiency anemia over a 3-year period were investigated. Ten patients had severe Trichuris trichiura infection and received a diagnosis of TDS. Colonoscopy and colonic biopsies. Patients received anthelmintic treatment, and their response was assessed. Ten patients with TDS were studied, including 8 female and 2 male patients with a mean (+/- standard deviation) age of 43 (+/- 15.5) years (range 15-65 years) and a hemoglobin level (+/- standard deviation) of 6.0 +/- 1.5 g/dL (range 4-8 g/dL); the duration (+/- standard deviation) of disease was 2.1 +/- 1.1 years (range 1.5-8.5 years). None of the patients had growth retardation, malnutrition, or immunodeficiency. Abdominal symptoms included abdominal pain, diarrhea, and hematochezia in 1 patient. Nine other patients had no abdominal symptoms. Colonoscopy revealed actively motile T. trichiura worms in large numbers in the right colon in 7 patients, in the ileum in 1, in the left colon in 1, and worms carpeting of the whole colonic mucosa in 1. Associated mucosal changes included petechial lesions, blotchy mucosal hemorrhages, and active mucosal oozing. Biopsy of the colon revealed worm segments with a thick outer cuticle. The posterior segment of the worm contained gravid uterus with numerous characteristic T. trichiura eggs. There was paucity of associated mucosal changes in most of the sections. Similar studies in other endemic areas are lacking. TDS should be considered in all patients in endemic areas with chronic iron deficiency anemia and/or occult blood loss.